rac-18-Meth-oxy-coronaridine hydro-chloride.

In the crystal structure of the racemic title compound, C(22)H(29)N(2)O(3) (+)·Cl(-), both NH groups form N-H⋯Cl hydrogen bonds with the chloride counter-ion, forming translational chains along the a axis.

Anti-HIV-1 activity of the Iboga alkaloid congener 18-methoxycoronaridine.

The Iboga alkaloid congener 18-methoxycoronaridine (18-MC) exhibits in vitro leishmanicidal and in vivo anti-addiction properties. In this paper, we describe that 18-MC inhibits HIV-1 infection in human peripheral blood mononuclear cells (PBMCs) and monocyte-derived macrophages. We found that 18-MC inhibits the replication of primary isolates of HIV-1 in a dose-dependent manner, regardless of the preferential chemokine receptor usage of the isolates, at non-cell-toxic concentrations. The antiretroviral activity of 18-MC resulted in EC (50) values of 22.5 +/- 4.7 microM and 23 +/- 4.5 microM for R5 and X4 isolates, respectively, in PBMCs, and a therapeutic index (TI) of 14.5. Similar findings were observed for inhibition of HIV-1 replication in macrophages: EC (50) equal to 12.8 +/- 5 microM and 9.5 +/- 3 microM for an R5 virus after 14 and 21 days of infection, respectively, with TI equal to 25.6 and 34.5. 18-MC moderately inhibits the HIV-1 enzyme reverse transcriptase (IC (50) = 69.4 microM), which at least partially explains its antiretroviral activity.

Novel iboga alkaloid congeners block nicotinic receptors and reduce drug self-administration.

18-Methoxycoronaridine, a novel iboga alkaloid congener, reduces drug self-administration in animal models of addiction. Previously, we proposed that these effects are mediated by the ability of 18-methoxycoronaridine to inhibit nicotinic alpha3beta4 acetylcholine receptors. In an attempt to identify more potent 18-methoxycoronaridine analogs, we have tested a series of 18-methoxycoronaridine congeners by whole-cell patch clamp recording of HEK 293 cells expressing recombinant nicotinic alpha3beta4 receptors or glutamate NR1/NR2B N-methyl-d-aspartate (NMDA) receptors. The congeners exhibited a range of inhibitory potencies at alpha3beta4 receptors. Five congeners had IC(50) values similar to 18-methoxycoronaridine, and all of these were ineffective at NMDA receptors. The congeners also retained their ability to reduce morphine and methamphetamine self-administration. These data are consistent with the importance of nicotinic alpha3beta4 receptors as a therapeutic target to modulate drug seeking. These compounds may constitute a new class of synthetic agents that act via the nicotinic alpha3beta4 mechanism to combat addiction.

Syntheses and biological evaluation of vinblastine congeners.

Sixty-two congeners of vinblastine (VLB), primarily with modifications of the piperidine ring in the carbomethoxycleavamine moiety of the binary alkaloid, were synthesized and evaluated for cytotoxicity against murine L1210 leukemia and RCC-2 rat colon cancer cells, and for their ability to inhibit polymerization of microtubular protein at < 10(-6) M, and for induction of spiralization of microtubular protein, and for microtubular disassembly at 10(-4) M concentrations. An ID50 range of >10(7) M concentrations was found for L1210 inhibition by these compounds, with the most active 1000x as potent as vinblastine.

Synthesis and biological evaluation of 18-methoxycoronaridine congeners. Potential antiaddiction agents.

Variation of the methoxycarbonyl and C-18 substituents of the antiaddictive compound 18-methoxycoronaridine, and contraction of its isoquinuclidine ring segment, provided 15 congeners for SAR evaluation at opioid and alpha3beta4 nicotinic acetylcholine receptors. The opioid activities were relatively low, and the alpha3beta4 nicotinic acetylcholine receptor activities were found to correlate with in vivo antiaddictive activities.

Interaction of tubulin with a new fluorescent analogue of vinblastine.

Vinblastine is an antimitotic agent that has been used extensively in cancer chemotherapy. The biological effects of the drug are believed to be the result of its interaction with tubulin, the major component of cellular microtubules. Fluorescence spectroscopy is a powerful and versatile technique for studying drug-tubulin interactions, but it rarely has been applied to studies involving vinca alkaloids. We have prepared a new fluorescent derivative of vinblastine designed to retain high affinity for tubulin while possessing a fluorophore that absorbs and emits visible light. A coumarin derivative of vinblastine, 17-deacetyl-O-(3-carbonylamino-7-diethylaminocoumarin) vinblastine (F-VLB), was prepared by reaction of 17-deacetylvinblastine with 7-diethylaminocoumarin-3-carbonyl azide. F-VLB was a potent inhibitor of in vitro microtubule assembly (IC(50) = 0.5 microM). F-VLB binding to tubulin was inhibited by vinblastine. Tubulin binding induced an increase in the F-VLB emission intensity and shifted the emission maximum to higher energy (from 500 to 480 nm). The Stokes shift of tubulin-bound F-VLB was about the same as the Stokes shift of the molecule in ethanol, indicating that the tubulin-bound fluorophore is probably on the exterior of the vinblastine binding site. Unlike vinblastine, F-VLB failed to induce self-assembly of tubulin that could be detected by light scattering or electron microscopy, although some self-association could be detected by analytical ultracentrifugation. Equilibrium binding parameters were quantitatively determined by monitoring the change in fluorescence anisotropy of F-VLB upon tubulin binding. The apparent equilibrium constant for F-VLB binding to tubulin [K(a)(app) = (7.7 +/- 0.5) x 10(4) M(-1) at 25 degrees C] was identical to the equilibrium constant for vinblastine binding to 2 microM tubulin (K(1)) measured under similar buffer and temperature conditions using ultracentrifugation [Vulevic, B., Lobert, S., and Correia, J. J. (1997) Biochemistry 36, 12828-12835]. Binding allocolchicine to tubulin did not significantly affect F-VLB's affinity for the protein [K(a)(app) = (9.1 +/- 0.4) x 10(4) M(-1) at 25 degrees C]. Analysis of the steady-state emission spectra yielded a distance between the colchicine and vinca binding sites on tubulin of approximately 40 A. F-VLB bound to paclitaxel- and glutaraldehyde-stabilized microtubules, with approximately equal affinity. We conclude that F-VLB can be used to obtain information about the vinblastine binding site on tubulin under equilibrium conditions.

Evidence for the locations of distinct steroid and Vinca alkaloid interaction domains within the murine mdr1b P-glycoprotein.

P-glycoproteins (P-gp) cause the efflux of a wide variety of unrelated hydrophobic compounds out of cells. However, the locations of the sites at which different classes of molecules initially interact with the protein are not well defined. A unique system was developed to search for P-gp drug-interaction domains using mutational analysis. The strategy is based upon identifying mutations that cause a decrease in the activity of P-gp inhibitors, which are structurally related to chemotherapeutic drugs transported by P-gps. Evidence of distinct steroid and taxane interaction domains has already been presented. The work reported here extends the study of the steroid interaction domain and presents evidence for a separate vinblastine interaction domain. A total of 10 steroid-related mutations, involving seven amino acids that are confined within transmembrane segments (TMS) 4 to 6, have been characterized. The location of these mutations indicates that steroids interact with the transporter within the inner leaflet of the plasma membrane. Four previously unidentified, Vinca-related mutations, involving three amino acids, have also been found. Unexpectedly, these mutations are clustered within an eight-amino acid segment proximal to the TMS-4 region. This portion of the protein is thought to be within the cytoplasmic compartment of the cell. Thus, the results suggest that at least part of the initial interaction between P-gp and Vinca alkaloids occurs in the cytoplasm. The steroid interaction domain does not extend into this region of the protein. However, this cytoplasmic section of the protein is likely to play an important role in promoting steroid transport.

In vitro activities of iboga alkaloid congeners coronaridine and 18-methoxycoronaridine against Leishmania amazonensis.

In previous studies, we demonstrated the leishmanicide effect of coronaridine, a natural indole alkaloid isolated from stem bark of Peschiera australis (Delorenzi et al., Antimicrob. Agents Chemother. 45:1349-1354, 2001). In this study we show the leishmanicidal effect of the synthetic coronaridine and its racemic 18-methoxylated analog, 18-methoxycoronaridine. Both alkaloids revealed a potent leishmanicide effect against Leishmania amazonensis, a causative agent of cutaneous and diffuse cutaneous leishmaniasis in the New World. Despite their potent leishmanicide effect, both alkaloids were neither toxic to murine macrophages nor did they modulate their oxidative or cytokine production responses.

Metabolism of 18-methoxycoronaridine, an ibogaine analog, to 18-hydroxycoronaridine by genetically variable CYP2C19.

18-Methoxycoronaridine, a newly developed ibogaine analog, has been reported to decrease the self-administration of morphine, cocaine, ethanol, and nicotine. It has also been reported to attenuate naltrexone-precipitated signs of morphine withdrawal. In this study, three metabolites of 18-methoxycoronaridine (18-MC) were separated and identified by high-performance liquid chromatography-electrospray ionization-mass spectrometry-mass spectrometry (HPLC-ESI-MS-MS); the major metabolite was 18-hydroxycoronaridine (18-HC). The other two metabolites were elucidated as hydroxylated metabolites on the basis of their MS-MS spectra. Catalytic studies of 18-MC O-demethylase activity in human liver microsomes indicate that one high affinity enzyme is involved in this reaction (K(m) from 2.81 to 7.9 microM; V(max) from 0.045 to 0.29 nmol/mg/min). In cDNA-expressing microsomes, only CYP2C19 displayed significant 18-MC O-demethylase activity (K(m) 1.34 microM; V(max) 0.21 nmol/mg/min). S-Mephenytoin, a selective CYP2C19 inhibitor, inhibited 18-MC O-demethylation by 65% at a concentration of 2 times its K(I), and antibodies against rat 2C (human CYP2C8, 2C9, 2C19) inhibited 18-HC formation by 70%. Studies with other cytochrome P450 (P450)-selective chemical inhibitors and antibodies failed to demonstrate an appreciable role for other P450s in this reaction. In addition, in microsomes from five different human livers, 18-MC O-demethylation correlated with S-mephenytoin 4'hydroxylase activity but not with other P450 probe reactions. These data indicate that 18-HC formation is the predominant pathway of 18-MC metabolism in vitro in human liver microsomes and that this metabolic pathway is primarily catalyzed by the polymorphic CYP2C19. The apparent selectivity of this pathway for CYP2C19 suggests 18-MC as a potentially useful probe of CYP2C19 activity in vitro and in vivo.

Syntheses of Strychnan- and Aspidospermatan-Type Alkaloids. 9.(1) The Enantioselective Generation of Tetracyclic ABCE Intermediates by a Tandem Condensation, [3,3]-Sigmatropic Rearrangement, and Cyclization Sequence.

Reactions of substituted acroleins with the tryptophan-derived benzyl 2-(benzylamino)-3-[3-[2-[(methoxycarbonyl)methyl]indolyl]]propionate gave tetracyclic hexahydro-1H-pyrrolo[2,3-d] intermediates with stereoselective placement of substituents for cyclization to pentacyclic Strychnos alkaloids. The benzyl ester moiety was readily removed by formation of a corresponding nitrile and reduction, thus providing enantioselective syntheses of the tetracyclic compounds.

Syntheses of Strychnos and Aspidospermatan-Type Alkaloids. 8. Selective Total Syntheses of Mossambine and 14-epi-Mossambine by a Radical Cyclization Reaction(1).

Mossambine (6) was obtained by a six-step reaction sequence from the indoloazepine ester 7. Radical cyclization of the tetracyclic vinyl iodide 12a provided a racemic pentacyclic ketone 16E, which could be converted to either enantiomer by condensation with (S or R)-N,S-dimethyl-S-phenylsulfoximine and selective pyrolysis of the resulting diastereomeric alcohols 18 and 19 or 20 and 21. Selective reductions of the resolved (or racemic) ketone 16E provided mossambine (6) and its hydroxy epimer 17.