Biocatalytic Cascade Synthesis of Enantioenriched Epoxides and Triols from Biomass-Derived Synthons Driven by Specifically Designed Enzymes

Multi-enzymatic cascades exploiting engineered enzymes are a powerful tool for the tailor-made synthesis of complex molecules from simple inexpensive building blocks. In this work, we engineered the promiscuous enzyme 4-oxalocrotonate tautomerase (4-OT) into an effective aldolase with 160-fold increased activity compared to 4OT wild type. Subsequently, we applied the evolved 4-OT variant to perform an aldol condensation, followed by an epoxidation reaction catalyzed by a previously engineered 4-OT mutant, in a one-pot two-step cascade for the synthesis of enantioenriched epoxides (up to 98% ee) from biomass-derived starting materials. For three chosen substrates, the reaction was performed at milligram scale with product yields up to 68% and remarkably high enantioselectivity. Furthermore, we developed a three-step enzymatic cascade involving an epoxide hydrolase for the production of chiral aromatic 1,2,3-prim,sec,sec-triols with high enantiopurity and good isolated yields. The reported one-pot, three-step cascade, with no intermediate isolation and being completely cofactor-less, provides an attractive route for the synthesis of chiral aromatic triols from biomass-based synthons.

Biocatalytic enantioselective hydroaminations enabling synthesis of N-arylalkyl-substituted L-aspartic acids

N-Substituted l-aspartic acids are important chiral building blocks for pharmaceuticals and food additives. Here we report the asymmetric synthesis of various N-arylalkyl-substituted l-aspartic acids using ethylenediamine-N,N'-disuccinic acid lyase (EDDS lyase) as a biocatalyst. This C-N lyase shows a broad non-natural amine substrate scope and outstanding enantioselectivity, allowing the efficient addition of structurally diverse arylalkylamines to fumarate to afford the corresponding N-arylalkyl-substituted l-aspartic acids in good isolated yield (up to 79%) and with excellent enantiopurity (>99% ee). These results further demonstrate that C-N lyases working in reverse constitute an extremely powerful synthetic tool to prepare difficult noncanonical amino acids.

Engineering of Multiple Modules to Improve Amorphadiene Production in Bacillus subtilis Using CRISPR-Cas9

Engineering strategies to improve terpenoids' production in Bacillus subtilis mainly focus on 2C-methyl-d-erythritol-4-phosphate (MEP) pathway overexpression. To systematically engineer the chassis strain for higher amorphadiene (precursor of artemisinin) production, a clustered regularly interspaced short palindromic repeat-Cas9 (CRISPR-Cas9) system was established in B. subtilis to facilitate precise and efficient genome editing. Then, this system was employed to engineer three more modules to improve amorphadiene production, including the terpene synthase module, the branch pathway module, and the central metabolic pathway module. Finally, our combination of all of the useful strategies within one strain significantly increased extracellular amorphadiene production from 81 to 116 mg/L after 48 h flask fermentation without medium optimization. For the first time, we attenuated the FPP-derived competing pathway to improve amorphadiene biosynthesis and investigated how the TCA cycle affects amorphadiene production in B. subtilis. Overall, this study provides a universal strategy for further increasing terpenoids' production in B. subtilis by comprehensive and systematic metabolic engineering.

Betacyanins, major components in Opuntia red-purple fruits, protect against acetaminophen-induced acute liver failure

Acetaminophen (APAP) misuse or overdose is the most important cause of drug-induced acute liver failure. Overdoses of acetaminophen induce oxidative stress and liver injury by the electrophilic metabolite N-acetyl-p-benzoquinone imine (NAPQI). Plant-based medicine has been used for centuries against diseases or intoxications due to their biological activities. The aim of this study was to evaluate the therapeutic value of Opuntia robusta and Opuntia streptacantha fruit extracts against acetaminophen-induced liver damage and to identify the major biocomponents on them. Opuntia fruit extracts were obtained by peeling and squeezing each specie, followed by lyophilization. HPLC was used to characterize the extracts. The effect of the extracts against acetaminophen-induced acute liver injury was evaluated both in vivo and in vitro using biochemical, molecular and histological determinations. The results showed that betacyanins are the main components in the analyzed Opuntia fruit extracts, with betanin as the highest concentration. Therapeutic treatments with Opuntia extracts reduced biochemical, molecular and histological markers of liver (in vivo) and hepatocyte (in vitro) injury. Opuntia extracts reduced the APAP-increased expression of the stress-related gene Gadd45b. Furthermore, Opuntia extracts exerted diverse effects on the antioxidant related genes Sod2, Gclc and Hmox1, independent of their ROS-scavenging ability. Therefore, betacyanins as betanin from Opuntia robusta and Opuntia streptacantha fruits are promising nutraceutical compounds against oxidative liver damage.

Antifungal and biofilm inhibitory effect of Cymbopogon citratus (lemongrass) essential oil on biofilm forming by Candida tropicalis isolates; an in vitro study

ETHNOPHARMACOLOGICAL RELEVANCE

Cymbopogon citratus (lemongrass) essential oil has been widely used as a traditional medicine and is well known for antimicrobial properties. Therefore, it might be a potent anti-infective and biofilm inhibitive against Candida tropicalis infections. Until now, no ideal coating or cleaning method based on an essential oil has been described to prevent biofilm formation of Candida strains on silicone rubber maxillofacial prostheses, voice prostheses and medical devices susceptible to C. tropicalis infections.

AIM OF THE STUDY

To investigate the antifungal and biofilm inhibitory effects of Cymbopogon citratus oil. Clinical isolates of C. tropicalis biofilms on different biomaterials were used to study the inhibitory effect.

MATERIALS AND METHODS

The efficacy of Cymbopogon citratus, Cuminum cyminum, Citrus limon and Cinnamomum verum essential oils were compared on biofilm formation of three C. tropicalis isolates on 24 well polystyrene plates. C. citratus oil coated silicone rubber surfaces were prepared using hypromellose ointment as a vehicle. The antifungal tests to determine minimum inhibitory and minimum fungicidal concentrations were assessed by a microbroth dilution method and biofilm formation was determined by a crystal violet binding assay.

RESULTS

C. tropicalis strains formed more biofilm on hydrophobic materials than on hydrophilic glass. C. citratus oil showed a high antifungal effect against all C. tropicalis strains. For comparison, C. limon oil and C. cyminum oil showed minor to no killing effect against the C. tropicalis strains. C. citratus oil had the lowest minimal inhibitory concentration of all essential oils tested and inhibited biofilm formation of all C. tropicalis strains. C. citratus oil coating on silicone rubber resulted in a 45-76% reduction in biofilm formation of all C. tropicalis strains.

CONCLUSION

Cymbopogon citratus oil has good potential to be used as an antifungal and antibiofilm agent on silicone rubber prostheses and medical devices on which C. tropicalis biofilms pose a serious risk for skin infections and may cause a shorter lifespan of the prosthesis.

Engineered C-N Lyase: Enantioselective Synthesis of Chiral Synthons for Artificial Dipeptide Sweeteners

Aspartic acid derivatives with branched N‐alkyl or N‐arylalkyl substituents are valuable precursors to artificial dipeptide sweeteners such as neotame and advantame. The development of a biocatalyst to synthesize these compounds in a single asymmetric step is an as yet unmet challenge. Reported here is an enantioselective biocatalytic synthesis of various difficult N‐substituted aspartic acids, including N‐(3,3‐dimethylbutyl)‐l‐aspartic acid and N‐[3‐(3‐hydroxy‐4‐methoxyphenyl)propyl]‐l‐aspartic acid, precursors to neotame and advantame, respectively, using an engineered variant of ethylenediamine‐N,N′‐disuccinic acid (EDDS) lyase from Chelativorans sp. BNC1. This engineered C–N lyase (mutant D290M/Y320M) displayed a remarkable 1140‐fold increase in activity for the selective hydroamination of fumarate compared to that of the wild‐type enzyme. These results present new opportunities to develop practical multienzymatic processes for the more sustainable and step‐economic synthesis of an important class of food additives.

Enantioselective Synthesis of Pharmaceutically Active γ-Aminobutyric Acids Using a Tailor-Made Artificial Michaelase in One-Pot Cascade Reactions

Chiral γ-aminobutyric acid (GABA) analogues represent abundantly prescribed drugs, which are broadly applied as anticonvulsants, as antidepressants, and for the treatment of neuropathic pain. Here we report a one-pot two-step biocatalytic cascade route for synthesis of the pharmaceutically relevant enantiomers of γ-nitrobutyric acids, starting from simple precursors (acetaldehyde and nitroalkenes), using a tailor-made highly enantioselective artificial “Michaelase” (4-oxalocrotonate tautomerase mutant L8Y/M45Y/F50A), an aldehyde dehydrogenase with a broad non-natural substrate scope, and a cofactor recycling system. We also report a three-step chemoenzymatic cascade route for the efficient chemical reduction of enzymatically prepared γ-nitrobutyric acids into GABA analogues in one pot, achieving high enantiopurity (e.r. up to 99:1) and high overall yields (up to 70%). This chemoenzymatic methodology offers a step-economic alternative route to important pharmaceutically active GABA analogues, and highlights the exciting opportunities available for combining chemocatalysts, natural enzymes, and designed artificial biocatalysts in multistep syntheses.

Modular Enzymatic Cascade Synthesis of Vitamin B5 and Its Derivatives

Access to vitamin B₅ [(R)‐pantothenic acid] and both diastereoisomers of α‐methyl‐substituted vitamin B₅ [(R)‐ and (S)‐3‐((R)‐2,4‐dihydroxy‐3,3‐dimethylbutanamido)‐2‐methylpropanoic acid] was achieved using a modular three‐step biocatalytic cascade involving 3‐methylaspartate ammonia lyase (MAL), aspartate‐α‐decarboxylase (ADC), β‐methylaspartate‐α‐decarboxylase (CrpG) or glutamate decarboxylase (GAD), and pantothenate synthetase (PS) enzymes. Starting from simple non‐chiral dicarboxylic acids (either fumaric acid or mesaconic acid), vitamin B₅ and both diastereoisomers of α‐methyl‐substituted vitamin B₅, which are valuable precursors for promising antimicrobials against Plasmodium falciparum and multidrug‐resistant Staphylococcus aureus, can be generated in good yields (up to 70 %) and excellent enantiopurity (>99 % ee). This newly developed cascade process may be tailored and used for the biocatalytic production of various vitamin B₅ derivatives by modifying the pantoyl or β‐alanine moiety.

Chemoenzymatic Synthesis and Pharmacological Characterization of Functionalized Aspartate Analogues As Novel Excitatory Amino Acid Transporter Inhibitors

Aspartate (Asp) derivatives are privileged compounds for investigating the roles governed by excitatory amino acid transporters (EAATs) in glutamatergic neurotransmission. Here, we report the synthesis of various Asp derivatives with (cyclo)alkyloxy and (hetero)aryloxy substituents at C-3. Their pharmacological properties were characterized at the EAAT1–4 subtypes. The l-threo-3-substituted Asp derivatives 13a–e and 13g–k were nonsubstrate inhibitors, exhibiting pan activity at EAAT1–4 with IC₅₀ values ranging from 0.49 to 15 μM. Comparisons between (dl-threo)-19a–c and (dl-erythro)-19a–c Asp analogues confirmed that the threo configuration is crucial for the EAAT1–4 inhibitory activities. Analogues (3b–e) of l-TFB-TBOA (3a) were shown to be potent EAAT1–4 inhibitors, with IC₅₀ values ranging from 5 to 530 nM. Hybridization of the nonselective EAAT inhibitor l-TBOA with EAAT2-selective inhibitor WAY-213613 or EAAT3-preferring inhibitor NBI-59159 yielded compounds 8 and 9, respectively, which were nonselective EAAT inhibitors displaying considerably lower IC₅₀ values at EAAT1–4 (11–140 nM) than those displayed by the respective parent molecules.

Cytotoxic Deoxypodophyllotoxin Can Be Extracted in High Purity from Anthriscus sylvestris Roots by Supercritical Carbon Dioxide

Deoxypodophyllotoxin is present in the roots of Anthriscus sylvestris. This compound is cytotoxic on its own, but it can also be converted into podophyllotoxin, which is in high demand as a precursor for the important anticancer drugs etoposide and teniposide. In this study, deoxypodophyllotoxin is extracted from A. sylvestris roots by supercritical carbon dioxide extraction. The process is simple and scalable. The supercritical carbon dioxide method extracts 75 - 80% of the total deoxypodophyllotoxin content, which is comparable to a single extraction by traditional Soxhlet. However, less polar components are extracted. The activity of the supercritical carbon dioxide extract containing deoxypodophyllotoxin was assessed by demonstrating that the extract arrests A549 and HeLa cells in the G₂/M phase of the cell cycle. We conclude that biologically active deoxypodophyllotoxin can be extracted from A. sylvestris by supercritical carbon dioxide extraction. The method is solvent free and more sustainable compared to traditional methods.

Acetyl-4'-phosphopantetheine is stable in serum and prevents phenotypes induced by pantothenate kinase deficiency

Coenzyme A is an essential metabolite known for its central role in over one hundred cellular metabolic reactions. In cells, Coenzyme A is synthesized de novo in five enzymatic steps with vitamin B5 as the starting metabolite, phosphorylated by pantothenate kinase. Mutations in the pantothenate kinase 2 gene cause a severe form of neurodegeneration for which no treatment is available. One therapeutic strategy is to generate Coenzyme A precursors downstream of the defective step in the pathway. Here we describe the synthesis, characteristics and in vivo rescue potential of the acetyl-Coenzyme A precursor S-acetyl-4′-phosphopantetheine as a possible treatment for neurodegeneration associated with pantothenate kinase deficiency.

Rapid chemoenzymatic route to glutamate transporter inhibitorl-TFB-TBOA and related amino acids

Rapid route tol-TFB-TBOA: Using only nine chemical transformations, we have managed to construct the complex amino acidl-TFB-TBOA starting from commercially available dimethyl acetylenedicarboxylate.

Stereochemical Control of Enzymatic Carbon-Carbon Bond-Forming Michael-Type Additions by "Substrate Engineering"

The enzyme 4-oxalocrotonate tautomerase (4-OT) promiscuously catalyzes the Michael-type addition of acetaldehyde to β-nitrostyrene derivatives to yield chiral γ-nitroaldehydes, which are important precursors for pharmaceutically active γ-aminobutyric acids. In this study, we investigated the effect of different substituents at the aromatic ring of the Michael acceptor on the catalytic efficiency and stereoselectivity of the 4-OT-catalyzed acetaldehyde addition reactions. Highly enantioenriched (R)- and (S)-γ-nitroaldehydes and 4-substituted chroman-2-ol could be obtained in good to excellent yields by applying different substituents at appropriate positions of the aromatic substrate. Stereochemical control of these enzymatic Michael-type additions by "substrate engineering" allowed the enantioselective synthesis of valuable γ-aminobutyric acid precursors. In addition, the results suggest a novel enzymatic synthesis route towards precursors for chromans and derivatives, which are valuable scaffolds for preparing biologically active natural products.

Using mutability landscapes of a promiscuous tautomerase to guide the engineering of enantioselective Michaelases

The Michael-type addition reaction is widely used in organic synthesis for carbon–carbon bond formation. However, biocatalytic methodologies for this type of reaction are scarce, which is related to the fact that enzymes naturally catalysing carbon–carbon bond-forming Michael-type additions are rare. A promising template to develop new biocatalysts for carbon–carbon bond formation is the enzyme 4-oxalocrotonate tautomerase, which exhibits promiscuous Michael-type addition activity. Here we present mutability landscapes for the expression, tautomerase and Michael-type addition activities, and enantioselectivity of 4-oxalocrotonate tautomerase. These maps of neutral, beneficial and detrimental amino acids for each residue position and enzyme property provide detailed insight into sequence–function relationships. This offers exciting opportunities for enzyme engineering, which is illustrated by the redesign of 4-oxalocrotonate tautomerase into two enantiocomplementary ‘Michaelases'. These ‘Michaelases' catalyse the asymmetric addition of acetaldehyde to various nitroolefins, providing access to both enantiomers of γ-nitroaldehydes, which are important precursors for pharmaceutically active γ-aminobutyric acid derivatives.

The Michael-type addition reaction is used for carbon-carbon bond formation; however biocatalytic methods for this reaction are rare. Here, the authors generate and exploit mutability landscapes of 4-oxalocrotonate tautomerase to direct the redesign of this promiscuous enzyme into enantio-complementary Michaelases.

The ER stress inducer DMC enhances TRAIL-induced apoptosis in glioblastoma

Glioblastoma multiforme (GBM) is the most aggressive malignant brain tumour in humans and is highly resistant to current treatment modalities. We have explored the combined treatment of the endoplasmic reticulum (ER) stress-inducing agent 2,5-dimethyl-celecoxib (DMC) and TNF-related apoptosis-inducing ligand (TRAIL WT) or the DR5-specific TRAIL D269H/E195R variant as a potential new strategy to eradicate GBM cells using TRAIL-resistant and -sensitive GBM cells. GBM cell lines were investigated for their sensitivity to TRAIL, DMC and combination of both agents. Cell viability was measured by MTS assay and apoptosis was assessed by Annexin V/PI and acridine orange staining. Caspase activation and protein expression levels were analysed with Western blotting. Death Receptor (DR) cell surface expression levels were quantified by flow cytometry. DR5 expression was increased in U87 cells by ectopic expression using a retroviral plasmid and survivin expression was silenced using specific siRNAs. We demonstrate that A172 expresses mainly DR5 on the cell surface and that these cells show increased sensitivity for the DR5-specific rhTRAIL D269H/E195R variant. In contrast, U87 cells show low DR cell surface levels and is insensitive via both DR4 and DR5. We determined that DMC treatment displays a dose-dependent reduction in cell viability against a number of GBM cells, associated with ER stress induction, as shown by the up-regulation of glucose-regulated protein 78 (GRP78) and CCAAT/-enhancer-binding protein homologous protein (CHOP) in A172 and U87 cells. The dramatic decrease in cell viability is not accompanied by a correspondent increase in Annexin V/PI or caspase activation typically seen in apoptotic or/and necrotic cells within 24h of treatment. Although DMC did not affect DR5 expression in the GBM cells, it increased TRAIL-induced caspase-8 activation in both TRAIL-sensitive and -resistant cells, indicating that DMC potentiates initiator caspase activation in these cells. In A172 cells, sub-toxic concentrations of DMC greatly potentiated TRAIL-induced apoptosis. Furthermore, DMC strongly reduced survivin expression in A172 and U87 cells and silencing of this anti-apoptotic protein partially sensitized cells to TRAIL-induced apoptosis. Our findings corroborate that DMC is a promising agent against GBM, and uncovers a potential synergistic cooperation with TRAIL in this highly malignant cancer.

Promiscuous catalysis of asymmetric Michael-type additions of linear aldehydes to β-nitrostyrene by the proline-based enzyme 4-oxalocrotonate tautomerase

Exploiting catalytic promiscuity: The proline-based enzyme 4-oxalocrotonate tautomerase (4-OT) promiscuously catalyzes asymmetric Michael-type additions of linear aldehydes--ranging from acetaldehyde to octanal--to trans-β-nitrostyrene in aqueous solvent. The presence of 1.4 mol% of 4-OT effected formation of the anticipated γ-nitroaldehydes in fair to good yields with dr values of up to 93:7 and ee values of up to 81 %.

New antipsychotic agents with serotonin and dopamine antagonist properties based on a pyrrolo[2,1-b][1,3]benzothiazepine structure

The development of a synthetic approach to the novel pyrrolo[2, 1-b][1,3]benzothiazepine and its derivatives and their biological evaluation as potential antipsychotic drugs are described. In binding studies these compounds proved to be potent 5-HT2, D2, and D3 receptor ligands. The more potent benzothiazepine (+/-)-3b was resolved into its enantiomers by using HPLC techniques. In vitro testing confirmed that (-)-3b is a more potent D2 receptor ligand, maintaining high affinity for 5-HT2 receptors. In contrast, the (+)-3b enantiomer presents a 35 times higher affinity for 5-HT2 than for dopamine D2 receptors with a similar dopamine D1 receptor affinity to that of (-)-3b. Overall, (+)-3b shows an "atypical" neuroleptic binding profile, while (-)-3b has a more "classical" profile. Furthermore pharmacological and biochemical testing displayed that the novel benzothiazepine (+/-)-3b is able to increase the extracellular levels of dopamine in the rat striatum and causes a dose-related suppression of apomorphine-induced locomotor activity. At low doses (+/-)-3b does not induce catalepsy, showing atypical antipsychotic properties similar to those of olanzapine. These heterocyclic compouds represent new leads for the development of novel antipsychotic drugs with atypical properties.

Affinity for dopamine D2, D3, and D4 receptors of 2-aminotetralins. Relevance of D2 agonist binding for determination of receptor subtype selectivity

A series of 2-aminotetralins, substituted with a methoxy or a hydroxy group on the 5- or 7-position, and with varying N-alkyl or N-arylalkyl substituents, were prepared and evaluated in binding assays for human dopamine (DA) D2, D3, and D4 receptors. Some members of this series were prepared in former studies, but were never tested in vitro with single receptor subtypes, and these were examined again. None of the tested 2-aminotetralins showed high affinity for the dopamine D4 receptor. However, a number of the 2-aminotetralins showed high affinity for both the D2 and the D3 DA receptors, as exemplified by compounds 11-15 and 21-26, while some had a reasonable selectivity for the DA D3 receptors. The affinities of the 2-aminotetralins for the D21, receptor depended on the type of radioligand (agonist or antagonist) used. The agonist affinity data, obtained by using the agonist ligand [3H]N-0437, are thought to be more relevant for calculating DA receptor subtype selectivity.

Affinities and intrinsic activities of dopamine receptor agonists for the hD21 and hD4.4 receptors

The affinity and intrinsic activity of dopamine receptor agonists were determined at the human dopamine hD21 and hD4.4 receptors. (-)-3-Hydroxy-N-n-propylpiperidine ((-)3-PPP) had an intrinsic activity of 46% and 83%, whereas (+)-N-propylnorapomorphine ((+)-NPA) had intrinsic activities of 61% and 58% at the dopamine hD21 and hD4.4 receptors, respectively. Affinities also varied. A single, or multiple, dopamine D2-type receptor(s) may be involved in schizophrenia and agonists are being tested as therapy. Understanding their properties at the individual dopamine D2-family receptors is important.

Thiamin deficiency impairs endotoxin-induced increases in hepatic glucose output

We addressed the role of thiamin, a cofactor for several enzymes involved in glucose metabolism, in the glucose metabolic response to endotoxin. Characterized by hyperglycemia, increased hepatic glucose production exceeding elevated rates of whole-body glucose utilization, this response is mediated by hormones and cytokines and is dependent on the immune and nutritional status of the host. We hypothesized that a thiamin-deficient state would impair the metabolic response to endotoxin. Rats were fed a thiamin-deficient or control diet for 6 wk before in vivo assessment of glucose kinetics. In control rats, Escherichia coli endotoxin increased the rate of glucose appearance (+76%), disappearance (+70%), and metabolic clearance (+50%). Thiamin deficiency resulted in increased plasma glucose (18%) and lactate (3- to 4-fold) as well as in a 30% decrease in insulin and an increase in glucagon (2.6-fold) and corticosterone (3.6-fold). Thiamin deficiency inhibited the endotoxin-induced hyperglycemia and the rise in hepatic glucose production, glucose utilization, and metabolic clearance rate.

Nutritional and metabolic characterization of a thiamine-deficient rat model

The effects of a thiamine-deficient diet on plasma and tissue vitamin concentrations and on whole-body glucose metabolism were assessed. Male Sprague-Dawley rats (175 to 200 g body weight) fed a thiamine-deficient (TD) or nutritionally complete purified diet were used for plasma thiamine mononitrate and monophosphate and for red blood cell and tissue thiamine pyrophosphate (TPP) determinations weekly for up to 5 weeks. Additional rats were used for assessment of basal glucose kinetics by using a primed constant infusion of [3-3H]glucose. Plasma thiamine mononitrate levels decreased 60% at 1 week and were undetectable after 5 weeks on the diet. Plasma thiamine monophosphate decreased 80% after 1 week on the TD diet, and levels were undetectable after 4 weeks on the diet. Red blood cell TPP in the TD group decreased progressively with time: 54% at 1 week, 86% at 3 weeks, and 92% at 5 weeks. At 1 and 4 weeks, the decrease in tissue TPP was significant in the liver (65% and 89%, respectively), gut (52% and 94%, respectively), spleen (40% and 60%, respectively), and skeletal muscle (37% and 76%, respectively), with the brain (7% and 84%, respectively) showing the slowest initial rate of depletion. The TD diet did not alter plasma glucose concentrations, but it increased plasma lactate by 75% and plasma pyruvate by 50% to 75%. Rates of hepatic glucose production and peripheral glucose utilization were not different between the control and TD rats at 2 weeks, but they were 25% higher in the TD rats after 6 weeks on the diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of the dopamine D2 agonist N-0923 and its major metabolites in perfused rat livers by HPLC-UV-atmospheric pressure ionization mass spectrometry

The metabolism of the dopamine D2 agonist N-0923 was investigated by an in vitro isolated liver perfusion. Determining the metabolic profile and identity of the different metabolites was achieved by using high-performance liquid chromatography with UV detection, combined with atmospheric pressure ionization mass spectrometry. Using this technique, no extensive sample cleanup is required, and the studies can be performed without radioactivity. In addition to previously observed metabolites, nine new metabolic products were identified. All metabolites were exclusively excreted into the bile, except for the despropyl metabolite, which was also detectable in the perfusate. 5-O-Glucuronidation and N-depropylation followed by 5-O-glucuronidation are the most important metabolic routes. N-dealkylation of the thienylethyl group followed by 5-O-glucuronidation and sulfation is a second major metabolic pathway. Catechol formation of the despropyl metabolite with or without subsequent conjugation was not found. Catechol formation of the desthienylethyl metabolite occurred, but only its glucuronide conjugates were found. This study complements previous results of in vivo metabolic studies using the radiolabeled racemate N-0437, and it explains differences in bile excretion during isolated liver perfusions using N-0923 and radiolabeled N-0923.

Central NMDA enhances hepatic glucose output and non-insulin-mediated glucose uptake by a nonadrenergic mechanism

One of the hallmarks of the stress response is an increased rate of hepatic glucose production (HGP) which, in conjunction with the presence of insulin resistance, leads to hyperglycemia. Excitatory amino acids (EAA) within the brain mediate some of the cardiovascular responses to stress, but their role in the hormonal and metabolic alterations is poorly defined. The aim of the present study was to determine whether the intracerebroventricular (i.c.v.) injection of either N-methyl-D-aspartate (NMDA) or kainate would produce metabolic alterations comparable to those observed under stress conditions. An i.c.v. cannula and vascular catheters were placed in rats prior to the experiment. After an overnight fast, HGP and peripheral glucose utilization (GU) were assessed in conscious unrestrained rats using [3-3H]glucose. Arterial glucose levels were increased 34% by 15 min after the i.c.v. injection of NMDA (1 microgram) and remained elevated throughout the 3-h protocol. The hyperglycemia resulted from an early increase in HGP (84%) that exceeded a smaller elevation (66%) in GU. The increased glucose flux was associated with sustained insulinopenia (-30%), and elevated levels of corticosterone (40-100%) and epinephrine (75-216%). The hormonal and glucose metabolic responses were quantitatively similar, although of shorter duration, in rats injected with kainate (10 ng). Intravenous adrenergic blockade completely prevented the NMDA-induced hyperglycemia. Adrenergic blockade blunted the early rise in HGP, so that in this group the NMDA-induced increase in HGP was offset by a comparable elevation in GU.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential control of glucoregulatory hormone response and glucose metabolism by NMDA and kainate

The aim of the present study was to elucidate the effect of kainate and N-methyl-D-aspartate (NMDA), two different excitatory amino acid (EAA) agonists, on glucoregulatory hormone production and whole body glucose metabolism. Rates of hepatic glucose production (HGP) and peripheral glucose utilization (GU) were assessed in overnight fasted, catheterized, conscious rats using [3-3H]glucose. At the highest dose of kainate examined (16 mg/kg), glucose levels increased 97% after 1 h; thereafter, glucose fell towards basal values but was still elevated 25% at the end of the 3 h experiment. This hyperglycemia resulted from a rapid increase in HGP that exceeded an increased rate of GU. Both HGP and GU were elevated 86% throughout the final 2 h of the experiment. NMDA induced changes in glucose flux that were qualitatively similar, yet of smaller magnitude and of shorter duration, than those produced by kainate. Kainate-induced increases in glucose metabolism were associated with an early transient hyperinsulinemia followed by a period of insulinopenia, and sustained increases in the plasma concentrations of glucagon, corticosterone, epinephrine and norepinephrine. In contrast, sustained increases in glucagon and catecholamines, as well as the late hypoinsulinemia were not detected in NMDA-treated rats. Adrenergic blockade attenuated the kainate- but not the NMDA-induced increase in glucose metabolism. These results indicate that EAA agonists that bind preferentially to different receptor subtypes produce qualitatively similar changes in glucose metabolism. Whereas the increased HGP in kainate-injected rats was associated with sustained elevations in glucagon, catecholamines and corticosterone, NMDA only transiently elevated circulating glucocorticoid levels, suggesting a different mechanism of action. These data, support the involvement of EAA in various aspects of glucoregulation.

Pharmacological aspects of R-(+)-7-OH-DPAT, a putative dopamine D3 receptor ligand

The R-(+)-isomer of 7-hydroxy-2-(N,N-di-n-propylamino)tetralin (7-OH-DPAT) bound with a more than 200-fold higher affinity to cloned human dopamine D3 receptors (Ki = 0.57 nM) than to dopamine D2 receptors; the corresponding S-(-)-enantiomer had considerably less affinity for both dopamine receptor subtypes, indicating that the known enantiomer selectivity of 7-OH-DPAT for the 'classical' dopamine D2 receptor subtype extends to the recently discovered dopamine D3 receptor subtype. In rats R-(+)-7-OH-DPAT dose dependently (10-1000 nmol/kg) decreased dopamine release and induced yawning, while sniffing behaviour occurred at the highest dose tested (1000 nmol/kg). The possibility that the inhibition of dopamine release and the elicitation of yawning are mediated by dopamine D3 receptors is considered.

Role of IL-1 alpha in central nervous system immunomodulation of glucoregulation

Hyperglycemia is a hallmark of the stress response, and has been largely attributed to elevated plasma levels of catabolic hormones. Recently, various cytokines have been shown to be endogenously produced within the brain and may represent an important component of the central regulation of this metabolic response. Therefore, the aim of the present study was to determine whether the intracerebroventricular (i.c.v.) injection of one such peptide, interleukin (IL)-1, can produce hormonal and metabolic alterations comparable to those observed under stress conditions. An i.c.v. cannula and vascular catheters were placed in rats prior to the experiment. Whole body glucose flux was assessed in overnight fasted conscious unrestrained rats using [3-3H]glucose. A mild hyperglycemia was elicited 20 min after the i.c.v. injection of IL-1 alpha (human recombinant, 100 ng) that was not detected in control rats. Glucose levels gradually increased and were 26% higher than control values during the last hour of the 3 h experimental period. The hyperglycemia resulted from a 44% increase in the rate of hepatic glucose output (HGO), which preceded a proportional rise in peripheral glucose utilization. No increase in metabolic clearance rate was observed, suggesting that the increased glucose uptake was the result of mass action. The increased glucose flux was associated with a transient hyperinsulinemia (+95%), and sustained elevations in the arterial concentrations of glucagon (56%) and corticosterone (175%). In contrast, glucose flux was not altered by intravenous administration of the same dose of IL-1 alpha, or i.c.v. injection of IL-1 beta, or heat-inactivated IL-1 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amido-8-methoxytetralins: a series of nonindolic melatonin-like agents

A series of unsubstituted and methoxy-substituted 2-amidotetralins (4a-q) was prepared and evaluated for their ability to compete for 2-[125I]iodomelatonin binding to chicken retinal membranes and for their potency to inhibit the calcium-dependent release of [3H]dopamine from rabbit retina. The lead compound, 2-acetamido-8-methoxytetralin (4j), showed a moderate affinity (Ki = 46 nM) and potency (IC50 = 1.4 nM) at the melatonin receptor. The structural requirements necessary for optimal agonistic activity at the melatonin receptor are as follows. First, the amido group, which should have a small, nonbranched alkyl group, is essential for affinity, and second, the methoxy substituent at the 8-position of the 2-amidotetralin ring is essential for optimal agonistic activity at the melatonin receptor. We concluded that this series of unsubstituted and methoxy-substituted 2-amidotetralins constitutes a class of nonindolic melatonin-like agents that can be used as pharmacological tools to further characterize melatonin receptors and to elucidate the mode of action of melatonin.

Enantiomers of monohydroxy-2-aminotetralin derivatives and their activity at dopamine autoreceptors as studied by brain dialysis

The enantiomers of a series of dopamine (DA) agonists, monohydroxy-2-aminotetralin derivatives, were investigated using brain microdialysis. We used a 5-OH-substituted derivative, N-0437 (2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin), and three 7-OH-substituted derivatives, N-0438 (2-(N-propyl-N-2-thienylethylamino)-7-hydroxytetralin), 7-OH-DPAT (7-hydroxy-2-(N,N-di-n-propylamino)tetralin) and PHNO (4-propyl-9-hydroxynaphthoxazine; position 9 of the naphtoxazines corresponds to position 7 of the aminotetralins). We studied the activity of the enantiomers at autoreceptors regulating the release of DA following their local infusion into the striatum of the rat. We were particularly interested in the activity of R(+)-N-0437, S(-)-N-0438, S(-)-7-OH-DPAT and S(-)-PHNO, which are enantiomers that have been classified as less potent or inactive in previous studies. S(-)-N-0437, R(+)-N-0438, R(+)-7-OH-DPAT and R(+)-PHNO decreased DA release by 45-60%. Thus, these enantiomers are potent agonists at autoreceptors regulating the release of DA. The R(+) enantiomer of the 5-OH-substituted derivative N-0437 possessed antagonistic activity at autoreceptors controlling DA release, increasing DA release by 100%. This finding is consistent with reports showing that one enantiomer of other 5-OH DA agonists displays agonistic activity, while the other has antagonistic properties at DA autoreceptors. The less potent enantiomers of the 7-OH-substituted derivatives S(-)-N-0438, S(-)-7-OH-DPAT and S(-)-PHNO, however, all showed weak agonistic activity at DA autoreceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological profile of non-hydroxylated and ether derivatives of the potent D2-selective agonist N-0437

Derivatives of the potent dopamine D2-selective agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0437) were designed, aimed at producing drugs with less sensitivity towards metabolic inactivation (in particular glucuronidation at the 5-OH position). Since aminotetralins with a 5-methoxy substituent or lacking the 5-hydroxy group have been reported to retain dopaminergic activity, the non-5-hydroxylated N-0437 (N-0918) and two ethers of N-0437 [5-methoxy-N-0437 (N-0724) and 5-cyclopentoxy-N-0437 (N-0953)] have been prepared and tested. Three indices for activity at central dopamine receptors are considered: (1) the displacement of (3H)-SCH-23390 and (3H)-spiperone from calf caudate membranes, (2) the effects on dopamine release and metabolism in the striatum of freely moving rats after systemic and intrastriatal administration as assessed by brain microdialysis, and (3) the ability to elicit contralateral turning in rats with a unilateral 6-OH-dopamine lesion of the nigrostriatal pathway. In order to differentiate between direct dopaminergic activity and metabolic activation, brain and plasma levels of N-0437 after administration of N-0724 and N-0953 were measured. The results show the necessity of the 5-OH group for direct dopaminergic activity: N-0918, N-0724 and N-0953 are all inactive after intrastriatal administration in the microdialysis model and all three drugs show a weak in vitro affinity for both D1 and D2 receptors. Although N-0918 is also inactive after systemic administration in the microdialysis and turning model, N-0724 and N-0953 do exhibit dopaminergic activity after systemic administration in these models.(ABSTRACT TRUNCATED AT 250 WORDS)

Orally active carbamate prodrugs of the selective dopamine agonist N-0437: in-vivo activities in the 6-OHDA turning model and in-vitro activities

The in-vivo activities of eight carbamate prodrugs of the D2-agonist N-0437 were determined by examining the effects of the prodrugs, after their oral administration in rats with unilateral 6-OHDA lesions of the striatum. The resulting contralateral turning was used as an index of the activity of the compounds. A comparison of the area under the curve of the time-effect curves of the prodrugs, revealed a significantly improved duration of action compared with N-0437 during the period 11-15 h after administration, for the propylcarbamate and the dimethoxyphenylcarbamate derivatives. The 2,4-dimethylphenylcarbamate showed a significantly enhanced turning behaviour over the whole 15 h time interval in comparison with N-0437. Three of the nine carbamates were virtually unhydrolysed in rat serum at 37 degrees C, while the other test compounds were hydrolysed relatively slowly, with t1/2 values ranging from 1.5-6 h. The test compounds differed greatly in partition coefficients, which were estimated by RP-HPLC (1-12 times more lipophilic than N-0437). The potential cholinesterase inhibiting properties of the carbamate prodrugs were assessed by a simple in-vitro incubation assay, which showed that only two carbamates were very weak cholinesterase inhibitors.

Transdermal administration of the dopamine agonist N-0437 and seven ester prodrugs: comparison with oral administration in the 6-OHDA turning model

The potent and selective D2-agonist N-0437 [2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin] undergoes considerable first-pass metabolism after oral administration due to glucuronidation of the phenolic group. In an attempt to improve its bioavailability, seven ester prodrugs of N-0437 were synthesized, i.e. the acetyl-, propionyl-, isobutyryl-, pivaloyl-, 2-amino-phenyl-, 2-methoxy-phenyl- and 2,4-dimethylphenyl-analogues. In vivo activities were assessed by measuring contralateral turning after transdermal administration of N-0437 and its prodrugs to rats with unilateral 6-OHDA lesions of the nigrostriatal pathway. From time-effect curves the area under the curve for separate time intervals was taken as a measure of dopaminergic activity during that interval. It was found that slowly hydrolyzing prodrugs, which are known to show an improved duration of action after oral administration, are devoid of activity after transdermal application. The acetyl-, the propionyl- and the isobutyryl analogues, which are prodrugs with a relatively high hydrolysis rate, were found to have interesting and promising profiles following transdermal application.

Metabolism and disposition of the dopamine agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin in conscious monkeys after subsequent i.v. oral, and ocular administration

The metabolism of 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0437) was investigated in conscious monkeys after subsequent i.v., oral, and ocular administration. The administration of the drug caused some physiological effects, such as bradycardia and sedation of the monkeys. During a collection period of 120 hr, on average 83% was recovered after iv administration and 90% after p.o. dosing. After i.v. administration, 44% was excreted in the bile, as compared to 38% in the urine and about 1% in the feces. After oral administration, bile is the major excretion route, accounting for about 60% of the dose, as compared to 25% in the urine and about 5% in the feces. After ocular administration, on average 62% was recovered after 7 hr, excreted in bile and urine in about equal amounts. All percentages given above reflect the total amount of radioactivity recovered, thus comprising the unchanged drug plus various metabolites. After all three dosing routes, N-0437 was metabolized almost completely prior to elimination. Direct glucuronidation of the phenolic group proved to be the major metabolic pathway of N-0437, comprising about 44% of the dose after i.v. and ocular administration and 72% after oral dosing. Hydroxylation of N-0437 at the position ortho to the phenolic group present yielded a catechol intermediate, which was excreted as a glucuronide and accounted for about 10% of the dose. In the monkey, a clear regioselective preference towards glucuronidation at the 6-position was observed. Besides the glucuronide, the sulfoconjugate of N-0437 was a major metabolite after i.v. and ocular administration, accounting for about 15% of the dose.(ABSTRACT TRUNCATED AT 250 WORDS)

The metabolic fate of the dopamine agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin in rats after intravenous and oral administration. II. Isolation and identification of metabolites

1. The in vivo metabolic pathways of 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (I) in rats have been established, using in vitro metabolism as a complementary technique. 2. All identified metabolites were conjugates. Glucuronidation at the phenolic group yields the major metabolite, accounting for 50% (i.v.) or 65% (oral) of the dose. The corresponding sulphate conjugate of I is virtually absent (less than 0.2% dose). 3. Hydroxylation of I, at the ortho position to the phenolic hydroxy group, yields 6-hydroxy-I (II), accounting for about 13% (i.v.) or 9% (oral) dose. This catechol is excreted, as a glucuronide, almost exclusively into the bile. Both the 5- and the 6-glucuronide of II were detected in about equal amounts. 4. Metabolism of I in vitro showed that under oxidative conditions, depropylation of I occurred. Conjugation of 3H-I in the presence of UDPGA or PAPS, was successful in yielding the glucuronide and sulphate conjugates.

The metabolic fate of the dopamine agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin in rats after intravenous and oral administration. I. Disposition and metabolic profiling

1. The disposition and metabolic profiling of 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin(I), a dopamine agonist, were studied in anaesthetized rats after i.v. administration and in non-anaesthetized rats after i.v. and oral dosing. No major differences due to narcosis were observed. 2. Independent of dosing route or anaesthetic, clearance of I was rapid. Bile was the main route of excretion, accounting for 88% dose, compared with 9% in urine. 3. Drug metabolic profiling revealed that I is almost completely metabolized before elimination; less than 0.5% total radioactivity in bile and urine was due to parent compound. 4. The biliary metabolic profiles after i.v. and oral administration were similar. One major metabolite was detected, accounting for 50% (i.v.) or 65% (oral) dose. The major biliary metabolite was identified as the glucuronide of I. 5. Urinary metabolic profiles were quantitatively different from those of bile. After i.v. administration one major metabolite was detected in urine, but this was not the major biliary metabolite. After oral administration, the major urine metabolite was the same as the major biliary metabolite. These differences can be explained by first-pass gastro-intestinal metabolism.

Improvement of the oral bioavailability of the selective dopamine agonist N-0437 in rats: the in vitro and in vivo activity of eight ester prodrugs

The potent and selective D2-agonist N-0437 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin undergoes considerable first-pass metabolism due to glucuronidation of the phenolic group after oral administration. In an attempt to improve the bioavailability, eight ester prodrugs of N-0437 were synthesized, i.e. the acetyl, isobutyryl, pivaloyl, benzoyl, 2-methylbenzoyl, 2-methoxybenzoyl, 2,4-dimethylbenzoyl and 2-aminobenzoyl analogues. To examine the hydrolysis rates of these compounds in vitro studies were performed in rat serum. The prodrugs showed a very diverse pattern of hydrolysis rates. The in vivo activities were determined by testing the prodrugs in rats with unilateral 6-OHDA lesions of the striatum. The resulting contralateral turning was used to measure the activity of the compounds. By calculating the area under the curve (AUC), of the time-effect curves of the prodrugs, a significantly improved duration of action was found for those prodrugs which have a slow in vitro hydrolysis rate. However no significant differences in total activity of these slowly hydrolysing prodrugs compared with N-0437 could be demonstrated, although the 2-aminobenzoyl and the 2,4-dimethylbenzoyl derivatives show interesting behavioural profiles. In contrast the isobutyryl ester, a prodrug with a relatively rapid hydrolysis rate, gave an improvement of turning behaviour over the whole time course in comparison with N-0437.

Stereoselective reversal of MPTP-induced parkinsonism in the marmoset after dermal application of N-0437

The selective dopamine D-2 receptor agonist N-0437 produced a rapid and dose-dependent reversal of motor deficits lasting 90-120 min following i.p. or oral administration of the racemate to MPTP-treated common marmosets. In contrast, topical application of (+/-)-, (+)- or (-)-N-0437 to the skin of MPTP-treated animals did not alter locomotor activity in the initial 4 h although other motor disabilities were reduced. However, 24 h following application of the racemate or the (-) enantiomer both locomotor activity and the other motor deficits induced by MPTP were improved. The increase in locomotor activity returned to basal values by 48-52 h following application of the racemate to the skin and by 72-76 h following administration of (-)-N-0437; the other motor deficits induced by MPTP were reduced for up to 72-76 h by both (+/-)- and (-)-N-0437. Application to skin of the (+) enantiomer produced no behavioural improvement or stimulation of locomotor activity. Transdermal administration of the active enantiomer of N-0437 may be of value in producing a prolonged reversal of parkinsonian motor deficits in man.

The enantiomers of the dopamine agonist N-0437: in vivo and in vitro effects on the release of striatal dopamine

The enantiomers of the potent and selective dopamine (DA) D-2 receptor agonist 2-(N-propyl-N-2-thienylethyl-amino)-5-hydroxytetralin, N-0437, were tested for their pharmacological actions on DA D-2 autoreceptors in vivo, by measuring DA release by microdialysis during local administration of both drugs and in vitro, by measuring their effects on the electrically stimulated release of [3H]DA from striatal slices. In both experimental situations (-)-N-0437, at low doses, acted as an agonist on receptors controlling DA release. However, in vivo at a concentration of 10 microM (-)-N-0437 induced a short-lasting increase in DA release and in vitro the inhibitory effect of (-)-N-0437 was significantly less pronounced at higher concentrations (1-10 microM). (+)-N-0437 (0.1-10 microM) showed an antagonistic action both in vivo and in vitro. Following inhibition of the neuronal impulse flow with tetrodotoxin, (+)-N-0437 failed to increase DA release suggesting the effect of this enantiomer is not associated with an amphetamine-like action on the nerve terminal. The use of the DA re-uptake inhibitor GBR 12909 confirmed the antagonism of (+)-N-0437 towards DA receptors. Since it is known that (+)-N-0437 acts as an agonist on DA D-2 autoreceptors controlling the synthesis of DA, these results provide additional evidence for the existence of distinct DA D-2 autoreceptor populations involved in the release and synthesis of DA. The differential actions of (-)- and (+)-N-0437 gave rise to mutual antagonism of the actions of the enantiomers both in vivo and in vitro, thus providing a strong argument for using the enantiomers instead of the racemate in clinical situations.

Affinity chromatography with the immobilized agonist N-0434 yields an active and highly purified preparation of the dopamine D-2 receptor from bovine striatum

Partial purification of the dopamine D-2 receptor from bovine striatum, solubilized in the presence of 1% digitonin, was obtained by chromatography on wheat germ lectin agarose. The preparation was purified approximately 10-fold. The stability of the receptor preparation was considerably improved and non-specific protein absorption on the affinity gel used later was decreased. Further purification was achieved on a column containing a D-2-selective agonist, N-0434. Approximately 90% of the receptor activity was bound to the gel and 20-40% of the activity could be eluted by pH shock. The total purification factor after one affinity chromatography step was estimated to be at least 1500. An active preparation of at least 20% purity was obtained after a second cycle of affinity chromatography. This corresponds to an enrichment of more than 5000 times compared to the solubilized receptor preparation.

Microdialysis and striatal dopamine release: stereoselective actions of the enantiomers of N-0437

An intracerebral dialysis method was used to test both enantiomers of the very potent and selective dopamine (DA) D-2 agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin, N-0437, for their actions on DA receptors in the striatum of the rat. (-)N-0437 induced a 60% decrease in DA release, which was independent of the presence or absence of a kainic acid lesion placed unilaterally in the striatum. Stereotyped behaviour was apparent following administration of the (-) enantiomer. Thus, (-)N-0437 displayed an agonistic action on both pre- and postsynaptic D-2 receptors. (+)N-0437 did not induce any effect in the release model after peripheral administration nor did it induce any form of stereotypy. A comparison between the effects of (-)N-0437 after oral (10 mumol/kg) and transdermal (10 mumol/kg) administration showed the advantages of the latter mode of administration. Transdermal application induced a much longer duration of action of the drug (13 h) in comparison with the oral mode (5 h). Thus, transdermal administration may be a very useful method of drug application for therapeutic use.

Determination of enantiomeric purity of the new D-2 dopamine agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0437) by reversed-phase high-performance liquid chromatography after pre-column derivatization with D(+)-glucuronic acid

This paper describes an enzymic derivatization procedure that allows accurate determination of very small amounts of enantiomeric impurities in the D-2 dopamine agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0437). After pre-column glucuronidation of the individual enantiomers, two diastereoisomers were formed which were separated by reversed-phase high-performance liquid chromatography. An enantiomeric purity of 99.84% was calculated for the (-)-enantiomer, against 99.89% for the (+)-enantiomer. The assay was validated by spiking 1% of the (-)-enantiomer in the (+)-enantiomer. A high accuracy (error 4.5%) and precision (coefficient of variation 2.9%, n = 5) of the method were established.

Synthesis and pharmacology of trans-4-n-propyl-3,4,4a,10b-tetrahydro-2H,5H-1-benzopyrano[4,3-b ]-1,4-oxazin-7- and -9-ols: the significance of nitrogen pKa values for central dopamine receptor activation

The 6-oxa analogues of potent dopamine agonists, hexahydronaphthoxazines (4a,4b), have been tested for dopamine receptor binding and stimulating activity and were found to be almost inactive. pKa value determinations indicated that these compounds are protonated to approximately 2%, while potent compounds are protonated to a much greater extent. These results strongly support the assumption that the protonated form of DA agonists is the active species at the receptor.

Pharmacological profile of N,N dipropyl-8-hydroxy-3-chromanamine, an oxygen isostere of the dopamine agonist N,N dipropyl-5-hydroxy-2-aminotetralin with enhanced presynaptic selectivity

The pharmacological profile of N,N dipropyl-8-hydroxy-3-chromanamine (DP-8OH-3CA), the oxygen isostere of N,N dipropyl-5-hydroxy-2-aminotetralin (DP-5OH-AT), was studied and the results compared to its carbon analogue and apomorphine. The chromanamine was found to displace the D2-dopaminergic ligand [3H] 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin with a higher potency than apomorphine and DP-5OH-AT; the IC50 values were 8, 11 and 16 nM, respectively. Experiments investigating the effects of these compounds on dopamine metabolism following oral (o.a.) and intraperitoneal administration (i.p.) showed that the chromanamine had an excellent o.a./i.p. ratio. The presynaptic actions on D2-dopamine receptors, which were studied using tyrosine hydroxylase inhibition, modulation of dopamine metabolism, prevention of alpha-methyl-p-tyrosine induced dopamine depletion in rats and hypomotility in mice, showed that the chromanamine acts as a D2-agonist with half maximal effects between 0.1 and 0.4 mumol/kg (i.p.) DP-8OH-3CA was found to evoke obvious postsynaptic effects when studied in such models as stereotyped behaviour, hyperlocomotion, turning behaviour in 6 hydroxydopamine lesioned rats and reserpine reversal. Stereotypy and the accompanying hyperlocomotion were found to be induced at a half maximal dose of 17 mumol/kg (i.p.). Both with the stereotyped and turning behaviours, a long duration of action was evident. The selectivity for presynaptic receptors was found to be 6.7 times higher than that of DP-5OH-AT, indicating that oxygen substitution can cause an enhancement of selectivity for presynaptic D2-dopamine receptors. Experiments on noradrenaline release and on serotonin synthesis showed that DP-8OH-3CA had only moderate affinity for 5-hydroxytryptamine and noradrenaline receptors. It is concluded that DP-8OH-3CA is a potent D2-agonist with an excellent o.a./i.p. ratio and enhanced selectivity for presynaptic dopamine receptors.