1-(2'-Bromobenzyl)-6,7-dihydroxy-N-methyl-tetrahydroisoquinoline and 1,2-Demethyl-nuciferine as Agonists in Human D2 Dopamine Receptors

Certain D₂-like dopamine receptor (DR) agonists are useful therapeutically as antiparkinsonian drugs, whereas D₂-like DR antagonists or partial agonists are proven effective as antipsychotics. Two isoquinoline derivatives, 1-(2'-bromobenzyl)-6,7-dihydroxy-N-methyl-tetrahydroisoquinoline (Br-BTHIQ, 1) and 1,2-demethyl-nuciferine (aporphine, 2), were herein synthesized, and their dopaminergic affinity in cloned human D₂R, D₃R, and D₄R subtypes and their behavior as agonists/antagonists were evaluated. They showed affinity values (K_i) for hD₂, hD₃, and hD₄ DR within the nanomolar range. The trends in affinity were hD₄R ≫ hD₃R > hD₂R for Br-BTHIQ (1) and hD₂R > hD₄R > hD₃R for 1,2-demethyl-nuciferine (2). The functional assays of cyclic adenosine monophosphate signaling at human D₂R showed a partial agonist effect for Br-BTHIQ (1) and full agonist behavior for aporphine (2), with half maximal effective concentration values of 2.95 and 10.2 μM, respectively. Therefore, both isoquinolines 1 and 2 have emerged as lead molecules for the synthesis of new therapeutic drugs that ultimately may be useful to prevent schizophrenia and Parkinson's disease, respectively.

Variation of Secondary Metabolites in the Aerial Biomass of Cryptocarya alba

Cryptocarya alba is an important tree species in the Chilean sclerophyllous forest. Its leaves and bark are used in traditional medicine to treat liver diseases and rheumatism. Analyses of the essential oil (EO) show serious discrepancies, and information on other constituents is limited. The aerial biomass of individual trees from 3 wild populations, some old trees, and farmed saplings were analyzed ( n = 132). The EO profiles were studied by gas chromatography/mass spectrometry (GC/MS). The alkaloidal and polyphenol compositions were determined by ultra-high-performance liquid chromatography (UHPLC)/MS-MS. The total polyphenol content, the total flavonoid content, and the antioxidant capacity (diphenylpicrylhydrazyl, azinobisethylbenzothiazolinesulfonic acid, and ferric reducing antioxidant power: DPPH, ABTS, and FRAP respectively) were determined by standard methods. Significant differences were found at the individual and population levels in the contents of polyphenols, total flavonoids, antioxidant capacity, and specific alkaloids for leaves, bark, and wood. Farmed saplings grown under less light showed higher concentrations of higenamine, N-methylcoclaurine, N-methyllaurotetanine, and isocorydine, while those receiving more light were richer in laurolitsine, boldine, coclaurine, catechin, quercetin, epicatechin, quercitrin, and procyanidins. Important variations were found according to the season, age of the tree and of the leaves. The EO composition also varied considerably. These results support the idea that the natural variability of medicinal species is an important subject for study.

Naturally occurring plant isoquinoline N-oxide alkaloids: their pharmacological and SAR activities

The present review describes research on novel natural isoquinoline alkaloids and their N-oxides isolated from different plant species. More than 200 biological active compounds have shown confirmed antimicrobial, antibacterial, antitumor, and other activities. The structures, origins, and reported biological activities of a selection of isoquinoline N-oxides alkaloids are reviewed. With the computer program PASS some additional SAR (structure-activity relationship) activities are also predicted, which point toward new possible applications of these compounds. This review emphasizes the role of isoquinoline N-oxides alkaloids as an important source of leads for drug discovery.

Purification and characterization of aporphine alkaloids from leaves of Nelumbo nucifera Gaertn and their effects on glucose consumption in 3T3-L1 adipocytes

Aporphine alkaloids from the leaves of Nelumbo nucifera Gaertn are substances of great interest because of their important pharmacological activities, particularly anti-diabetic, anti-obesity, anti-hyperlipidemic, anti-oxidant, and anti-HIV’s activities. In order to produce large amounts of pure alkaloid for research purposes, a novel method using high-speed counter-current chromatography (HSCCC) was developed. Without any initial cleanup steps, four main aporphine alkaloids, including 2-hydroxy-1-methoxyaporphine, pronuciferine, nuciferine and roemerine were successfully purified from the crude extract by HSCCC in one step. The separation was performed with a simple two-phase solvent system composed of n-hexane-ethyl acetate-methanol-acetonitrile-water (5:3:3:2.5:5, v/v/v/v/v). In each operation, 100 mg crude extracts was separated and yielded 6.3 mg of 2-hydroxy-1-methoxyaporphine (95.1% purity), 1.1 mg of pronuciferine (96.8% purity), 8.5 mg of nuciferine (98.9% purity), and 2.7 mg of roemerine (97.4%) respectively. The chemical structure of four aporphine alkaloids are identified by means of electrospray ionization MS (ESI-MS) and nuclear magnetic resonance (NMR) analysis. Moreover, the effects of four separated aporphine alkaloids on insulin-stimulated glucose consumption were examined in 3T3-L1 adipocytes. The results showed that 2-hydroxy-1-methoxyaporphine and pronuciferine increased the glucose consumption significantly as rosiglitazone did.

LC/MS guided isolation of alkaloids from lotus leaves by pH-zone-refining counter-current chromatography

The traditional methods used in natural product separation primarily target the major components and the minor components may thus be lost during the separation procedure. Consequently, it's necessary to develop efficient methods for the preparative separation and purification of relatively minor bioactive components. In this paper, a LC/MS method was applied to guide the separation of crude extract of lotus (Nelumbo nucifera Gaertn.) leaves whereby a minor component was identified in the LC/MS analysis. Afterwards, an optimized pH-zone-refining CCC method was performed to isolate this product, identified as N-demethylarmepavine. The separation procedure was carried out with a biphasic solvent system composed of hexane-ethyl acetate-methyl alcohol-water (1:6:1:6, v/v) with triethylamine (10 mM) added to the upper organic phase as a retainer and hydrochloric acid (5 mM) to the aqueous mobile phase eluent. Two structurally similar compounds--nuciferine and roemerine--were also obtained from the crude lotus leaves extract. In total 500 mg of crude extract furnished 7.4 mg of N-demethylarmepavine, 45.3 mg of nuciferine and 26.6 mg of roemerine with purities of 90%, 92% and 96%, respectively. Their structures were further identified by HPLC/ESI-MSn, FTICR/MS and the comparison with reference compounds.

Simplified tetrandrine congeners as possible antihypertensive agents with a dual mechanism of action

A series of O- and/or N-substituted derivatives of (+/-)-coclaurine (1a) were synthesized as simplified structural mimics of the antihypertensive alkaloid tetrandrine (2) and assayed for binding to brain cortical sites labeled with the alpha(1)-adrenergic radioligand [(3)H]prazosin or the calcium channel radioligand [(3)H]diltiazem. The introduction of O-benzyl groups on the coclaurine molecule, which exhibits only adrenergic antagonist activity, led to the appearance of calcium channel blocking activity comparable to that of tetrandrine while retaining adrenolytic activity in the same concentration range. Contraction of aortal rings with noradrenaline or KCl was relaxed more potently by some of these coclaurine derivatives than by tetrandrine, suggesting leads for the development of novel antihypertensive drugs with a dual mechanism of action.