Tuck-Meng Lim

Tronocarpine, a novel pentacyclic indole incorporating a seven-membered lactam moiety

Abstract A novel pentacyclic indole alkaloid, tronocarpine, incorporating a seven-membered lactam unit, was obtained from the stem-bark extract of Tabernaemontana corymbosa and its structure elucidated by spectral analysis.

Biologically active indole and bisindole alkaloids from Tabernaemontana divaricata

The ethanol extract of the leaves of Tabernaemontana divaricata (double flower variety) provided a total of 23 alkaloids, including the new aspidosperma alkaloids, taberhanine, voafinine, N-methylvoafinine, voafinidine, voalenine and the new bisindole alkaloid, conophyllinine in addition to the previously known, biologically active bisindole, conophylline and its congener, conofoline. The structures of the new alkaloids were established by spectroscopic methods. The preparation and characterization of the corresponding quinones of the biologically active bisindoles are also described in relation to a structure-activity study of these compounds with respect to their action in stimulating insulin expression.

Voastrictine, a novel pentacyclic quinolinic alkaloid from Tabernaemontana

Abstract A novel pentacyclic quinolinic alkaloid, voastrictine, was obtained from Tabernaemontana corymbosa and its structure elucidated by spectroscopic analysis.

TRONOHARINE, A NOVEL HEXACYCLIC INDOLE ALKALOID FROM A MALAYAN TABERNAEMONTANA

Abstract A novel hexacylic indole alkaloid, tronoharine, was obtained from the stem-bark extract of Tabernaemontana corymbosa and its structure elucidated by spectral analysis.

Structure and biomimetic, electrochemically-mediated semisynthesis of the novel pentacyclic indole danuphylline

Abstract The structure of the novel pentacyclic indole, danuphylline, from Kopsia dasyrachis was established by spectral analysis. Anodic oxidation of the hexacylic alkaloid methyl 11,12-methylenedioxychanofruticosinate on platinum in TEAP/MeCN-CH2Cl2 (2 F mol−1) yielded an iminium ion salt which on silica gel chromatography underwent a facile retro-aldol process to give danuphylline. Allowing the oxidation to proceed until consumption of 4 F mol−1 of charge resulted in an unprecedented electrochemically-mediated aromatic chlorination yielding 10-chlorodanuphylline.

Mersinines A and B and mersiloscine, novel quinolinic alkaloids from Kopsia

Abstract Three novel quinolinic alkaloids, viz., mersinines A and B and mersiloscine, were obtained from a Malayan Kopsia species and the structures established by spectroscopic analysis.

ELECTROCHEMICAL OXIDATION OF ASPIDOFRACTININE-TYPE INDOLE ALKALOIDS. A FACILE, ELECTROCHEMICALLY-MEDIATED CONVERSION OF KOPSINGINE TO KOPSIDINES A, B, C AND KOPSINGANOL

Abstract Kopsidine A, B, C and kopsinganol were synthesised from kopsingine in good yields via the stable imminium salt obtained from electrochemical oxidation of kopsingine. Electrooxidation of dihydrokopsingine on the other hand gave the 17-to-5 and 17-to-3 oxo-bridged alkaloids directly, while 3-oxokopsingine was inert to electrooxidation in the potential range employed.

17-α-Hydroxy-Δ14,15-kopsinine and a bisindole alkaloid from Kopsia teoi

Abstract The structure of 17-α-hydroxy-Δ14,15-kopsinine has been confirmed by a detailed NMR analysis. A bisindole alkaloid was obtained from the leaf extract of Kopsia teoi and its structure established by spectral methods.

Danuphylline, a novel pentacyclic indole from Kopsia

Abstract A novel pentacyclic indole alkaloid, danuphylline, was obtained from the leaf-extract of Kopsia dasyrachis and its structure elucidated by spectral analysis.

Electron-transfer versus nucleophilic substitution in the reactions of α-halogenated 4-nitrotoluenes with base

A comparative study of the reactions of 4-nitrobenzyl and 4-nitrobenzylidene halides (ArCHXY; Ar = 4-NO2C6H4–; X = H or Halogen; Y = Halogen) with alkali shows that the reaction is sensitive to the nature of the side chain halogen substituent(s) as well as the reaction conditions. In alcoholic alkali, only 4-nitrobenzyl chloride (ArCH2Cl) reacts smoothly via the electron transfer (ET)-radical pathway to give mainly dimeric products while the corresponding bromide (ArCH2Br) and iodide (ArCH2I) give exclusively SN products. The ET pathway is enhanced for these substrates by the application of phase-transfer catalysis. In the case of the 4-nitrobenzylidene dihalides (ArCHXY; X = Y = Cl; X = Cl, Y = Br; X = Y = Br; X = F, Y = Br) it is also shown that although progressive bromine substitution suppresses the ET pathway, application of phase-transfer catalysis minimises competing solvolytic reactions and enhances the radical reaction.