Effects of two-carbon bridge region methoxylation of benztropine: discovery of novel chiral ligands for the dopamine transporter

Microbial transformation of 3β-acetoxypregna-5,16-diene-20-one by Penicillium citrinum

The biotransformation of 3β-acetoxypregna-5,16-diene-20-one (1) by using a filamentous fungus Penicillium citrinum resulted in the production of four metabolites 2-5. The structures of these compounds were elucidated by different spectroscopic analysis (1D- and 2D-NMR) and HR-ESI-MS as 3β,7β-dihydroxy-pregn-5,16(17)-dien-20-one (2), 3β-hydroxy-7α-methoxy-pregn-5,16(17)-dien-20-one (3), 3β,7β,11α-trihydroxy-pregn-5,16(17)-dien-20-one (4), and a known 3β,7α-dihydroxy-pregn-5,16(17)-dien-20-one (5). The 7-O-methylation is a novel reaction in the field of microbial transformation of pregnane steroids.

New microbiological transformations of steroids by Streptomyces virginiae IBL-14

A bacterium Streptomyces virginiae IBL-14 capable of effective degradation of diosgenin was isolated from activated sludge for treatment of waste from a steroidal drug factory. From the culture broth of diosgenin degradation, 11 compounds were purified and then identified, eight of which were previously unidentified compounds including 1-dehydroisonuatigenone [VI], nuatigenone [VIII], 1-dehydronuatigenone [X], 26-acetyl-nuatigenone [XII], 6-methoxy-6-dehydrodiosgenone [XIII], 6-methoxy-6-dehydroisonuatigenone [XIV], 6-methoxy-6-dehydronuatigenone [XV], and 6-dimethoxy-7alpha-hydroxyldiosgenone [XVI]. Additionally, two important microbial transformations of diosgenin (6-methoxylation and C25-tertiary carbon hydroxylation) were found. Two valuable chemical reactions of the steroids (structural rearrangement and esterification)were also confirmed. As a result, a new metabolic pathway of diosgenin metabolism was postulated.

N-8-Substituted benztropinamine analogs as selective dopamine transporter ligands

A series of N-8-substituted benztropinamines was synthesized and evaluated for binding at the dopamine (DAT), serotonin (SERT), norepinephrine (NET) transporters, and muscarinic M1 receptors. In general, the isosteric replacement of the C-3 benzhydrol ether of benztropine by a benzhydryl amino group was well tolerated at the DAT. However, for certain N-8 substituted derivatives, selectivity over muscarinic M1 receptor affinity was reduced.

Recognition of benztropine by the dopamine transporter (DAT) differs from that of the classical dopamine uptake inhibitors cocaine, methylphenidate, and mazindol as a function of a DAT transmembrane 1 aspartic acid residue

Binding of cocaine to the dopamine transporter (DAT) protein blocks synaptic dopamine clearance, triggering the psychoactive effects associated with the drug; the discrete drug-protein interactions, however, remain poorly understood. A longstanding postulate holds that cocaine inhibits DAT-mediated dopamine transport via competition with dopamine for formation of an ionic bond with the DAT transmembrane aspartic acid residue D79. In the present study, DAT mutations of this residue were generated and assayed for translocation of radiolabeled dopamine and binding of radiolabeled DAT inhibitors under identical conditions. When feasible, dopamine uptake inhibition potency and apparent binding affinity K(i) values were determined for structurally diverse DAT inhibitors. The glutamic acid substitution mutant (D79E) displayed values indistinguishable from wild-type DAT in both assays for the charge-neutral cocaine analog 8-oxa-norcocaine, a finding not supportive of the D79 "salt bridge" ligand-docking model. In addressing whether the D79 side chain contributes to the DAT binding sites of other portions of the cocaine pharmacophore, only inhibitors with modifications of the tropane ring C-3 substituent, i.e., benztropine and its analogs, displayed a substantially altered dopamine uptake inhibition potency as a function of the D79E mutation. A single conservative amino acid substitution thus differentiated structural requirements for benztropine function relative to those for all other classical DAT inhibitors. Distinguishing the precise mechanism of action of this DAT inhibitor with relatively low abuse liability from that of cocaine may be attainable using DAT mutagenesis and other structure-function studies, opening the door to rational design of therapeutic agents for cocaine abuse.

Synthesis and Pharmacology of 6-Substituted Benztropines: Discovery of Novel Dopamine Uptake Inhibitors Possessing Low Binding Affinity to the Dopamine Transporter

A series of 6alpha- and 6beta-substituted benztropines were synthesized. A marked enantioselectivity was observed for the 6beta-methoxylated benztropines, the (1R)-isomers being more potent than the corresponding (1S) compounds. The racemic 6alpha-methoxy-3-(4',4' '-difluorodiphenylmethoxy)tropane (5 g) was the most potent compound. It has been found that modifications at the 6-position of benztropine might reduce the DAT binding affinity, maintaining otherwise a significant dopamine uptake inhibitory activity. A reinvestigation of the absolute configuration of 6beta-methoxytropinone proved the 6R configuration for the (+)-enantiomer.

The effect of 6-substituted-4',4"-difluorobenztropines on monoamine transporters and the muscarinic M1 receptor

A series of racemic 6-hydroxy and carboalkoxy substituted-4('),4"-difluorobenztropines was synthesized and evaluated for binding at the dopamine (DAT), the serotonin (SERT), the norepinephrine (NET) transporters, and the muscarinic M1 receptor. Each of the analogues displaced [(3)H]WIN 35,428 (DAT) with a range of affinities from 5.81 to 175 nM and [(3)H]pirenzepine (M1), with a range of affinities ( K(i)= -8430 nM). Binding affinities at the SERT and the NET were generally low.

Structural requirements for 2,4- and 3,6-disubstituted pyran biomimetics of cis-(6-benzhydryl-piperidin-3-yl)-benzylamine compounds to interact with monoamine transporters

In our effort to delineate novel pharmacophoric configuration of bioisosteric pyran versions of cis-(6-benzhydryl-piperidin-3-yl)-benzylamine derivatives in interacting with the monoamine transporter, further structure-activity relationship study was carried out. Both cis and trans 2,4- and 3,6-disubstituted derivatives were synthesized to determine the positional importance of N-substitution on affinity for monoamine transporters, that is the dopamine transporter (DAT), the serotonin transporter (SERT), and the norepinephrine transporter (NET) in rat brain. For that purpose, the potency of compounds was determined in competing for the binding of [(3)H]WIN 35,428, [(3)H]citalopram, and [(3)H]nisoxetine, respectively. Selected compounds were also evaluated for their activity in inhibiting the uptake of [(3)H]DA by DAT. Our binding results demonstrated potency in 3,6-disubstituted derivatives while 2,4-disubstituted derivatives failed to exhibit any appreciable binding affinity. Further structural exploration of the exocyclic N-atom in 3,6-disubstituted derivatives produced compounds potent at both DAT and NET. Compounds 16h and 16o with hydroxyl and amino groups in the phenyl moiety of the benzyl group produced the highest activity for the NET. In this regard, compound 16e with a methoxy substituent produced weak affinity at NET, which upon conversion into a hydroxyl functionality as in 16h produced potent affinity for the NET. Various indole derivatives displayed different interactions; the 5-substituted indole derivative 16n exerted potent affinity for NET, confirming the bioisosteric equivalence between this indole moiety and the phenyl-4-hydroxy group in 16h.

Design, synthesis, and activity of novel cis- and trans-3,6-disubstituted pyran biomimetics of 3,6-disubstituted piperidine as potential ligands for the dopamine transporter

In our effort to develop novel molecules for the dopamine transporter, we converted our previously designed dopamine transporter specific 3,6-disubstituted piperidine template into corresponding pyran derivatives. cis-Pyran derivative 7b, like their piperidine counterparts, exhibited greater activity for the dopamine transporter compared to the trans-isomer. Further molecular modifications of the cis derivative led to the development of potent analogues which indicated successful bioisosteric replacement of the piperidine ring by a pyran moiety in these 3,6-disubstituted derivatives.

Probes for the dopamine transporter: new leads toward a cocaine-abuse therapeutic--A focus on analogues of benztropine and rimcazole

In an attempt to discover a cocaine-abuse pharmacotherapeutic, extensive investigation has been directed toward elucidating the molecular mechanisms underlying the reinforcing effects of this psychostimulant drug. The results of these studies have been consistent with the inhibition of dopamine uptake, at the dopamine transporter (DAT), which results in a rapid and excessive accumulation of extracellular dopamine in the synapse as being the mechanism primarily responsible for the locomotor stimulant actions of cocaine. Nevertheless, investigation of the serotonin (SERT) and norepinephrine (NET) transporters, as well as other receptor systems, with which cocaine either directly or indirectly interacts, has suggested that the DAT is not solely responsible for the reinforcing effects of cocaine. In an attempt to further elucidate the roles of these systems in the reinforcing effects of cocaine, selective molecular probes, in the form of drug molecules, have been designed, synthesized, and characterized. Many of these compounds bind potently and selectively to the DAT, block dopamine reuptake, and are behaviorally cocaine-like in animal models of psychostimulant abuse. However, there have been exceptions noted in several classes of dopamine uptake inhibitors that demonstrate behavioral profiles that are distinctive from cocaine. Structure-activity relationships between chemically diverse dopamine uptake inhibitors have suggested that different binding interactions, at the molecular level on the DAT, as well as divergent actions at the other monoamine transporters may be related to the differing pharmacological actions of these compounds, in vivo. These studies suggest that novel dopamine uptake inhibitors, which are structurally and pharmacologically distinct from cocaine, may be developed as potential cocaine-abuse therapeutics.

Enantioselective synthesis of S-(+)-2beta-carboalkoxy-3alpha-[bis(4-fluorophenyl)methoxy]tropanes as novel probes for the dopamine transporter

Synthesis of a series of pure S-(+)-2beta-carboalkoxy-3alpha-[bis(4-fluorophenyl)methoxy]tropanes (>99% ee) was achieved by employing a chiral amine-induced asymmetric reaction of tropinone with methyl cyanoformate as the key step. In this series, all of the S-(+)-enantiomers were 2-fold more potent than their racemic mixtures and all displayed high-affinity binding for DAT (K(i)=13-40 nM). These data support previous findings of significant divergence in structural requirements for high-affinity DAT binding among tropane-based inhibitors. Furthermore, the 2-substituent in the 3alpha-[bis(4-fluorophenyl)methoxy]tropane series is well tolerated at the DAT but not at SERT (K(i)=690-2040 nM), or muscarinic M(1) receptors (K(i)=133-4380 nM) resulting in highly selective DAT ligands that may provide new leads toward a cocaine-abuse therapeutic.