David W. Gammon

Bioactive alkaloids from Brunsvigia radulosa.

A phytochemical investigation of the bulbs of Brunsvigia radulosa yielded the new alkaloid 1-O-acetylnorpluviine, together with the known structures 1-epideacetylbowdensine, crinamine, crinine, hamayne, lycorine, anhydrolycorin-6-one and sternbergine. All structures were established by spectroscopic evidence. Some of the 13C assignments which were reported for crinamine and hamayne were corrected by means of 2D NMR techniques. In order to provide a further structure for biological testing, crinamine was converted to apohaemanthamine. The alkaloids were tested for activity against two strains of cultured Plasmodium falciparum and for cytotoxicity with BL6 mouse melanoma cells.

Mechanistic Insight into the Conversion of Tetrose Sugars to Novel α‐Hydroxy Acid Platform Molecules

α‐Hydroxy acids (AHAs) such as lactic acid are considered platform molecules in the biorefinery concept and have high‐end applications in solvents and biodegradable polyester plastics. The synthesis of AHAs with a four‐carbon backbone structure is a recently emerging field. New biomass‐related routes towards their production could stimulate their practical use in new polyester plastics. Herein, we report the unique catalytic activity of soluble tin metal salts for converting tetroses, namely erythrulose and erythrose, into new four‐carbon‐backbone AHAs such as methyl vinylglycolate and methyl‐4‐methoxy‐2‐hydroxybutanoate. An in situ NMR study together with deuterium labeling experiments and control experiments with intermediates allowed us to propose a detailed reaction pathway.

Anti-mycobacterial activity of five plant species used as traditional medicines in the Western Cape Province (South Africa)

ETHNOPHARMACOLOGICAL RELEVANCE Five plants used in traditional medicine in the Western Cape Province of South Africa, have been investigated for anti-mycobacterial activity: Olea capensis, Tulbaghia alliacea, Dittrichia graveolens, Leysera gnaphalodes and Buddleja saligna. AIM OF THE STUDY The aim was to assess antimycobacterial activity in plants used in treatment of symptoms of TB, and through activity-guided fractionation of extracts to isolate compounds or mixtures with potential as anti-TB drug leads. MATERIALS AND METHODS Extracts and derived fractions were assayed against strains of Escherichia coli, Staphylococcus aureus, and Mycobacterium aurum A+. Isolated pure compounds were further tested against Mycobacterium species M. avium ATCC 25291, M. scrofulaceum ATCC 19981, M. microti ATCC 19422 and Mtb H37Rv, and for cytotoxicity against Chinese hamster ovarian cells. RESULTS Extracts of B. saligna and L. gnaphaloides exhibited significant anti-mycobacterial activity, primarily associated with the presence of non-cytotoxic triterpenoids oleanolic acid in B. saligna and both oleanolic and ursolic acids in L. gnaphaloides. CONCLUSIONS Anti-mycobacterial activity of extracts of selected plants is consistent with their traditional use. The identification of oleanolic and ursolic acids in these plants, and verification of their activity, underlines the potential for exploring structure-activity relationships of derivatives of these ubiquitous triterpenoids.

Alkaloids from Crinum delagoense

Abstract Six alkaloids have been isolated from fresh bulbs of Crinum delagoense . The alkaloids, delagoensine and delagoenine, are reported here for the first time. The structure and stereochemistry of the new alkaloids have been determined by physical and spectroscopic methods. 1 H and 13 C NMR spectra were completely assigned by means of 2D NMR techniques.

Synthesis of mycothiol, 1D-1-O-(2-[N-acetyl-l-cysteinyl]amino-2-deoxy-α-d-glucopyranosyl)-myo-inositol, principal low molecular mass thiol in the actinomycetes

Members of the actinomycetes produce 1D-1-O-(2-[N-acetyl-L-cysteinyl]amino-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol or mycothiol 1 as principal low molecular mass thiol. Chemical synthesis of a biosynthetic precursor of mycothiol, the pseudodisaccharide 1D-1-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol 13 was achieved by the following steps: (1) Enantioselective synthesis gave the glycosyl acceptors (-)-2,3,4,5,6-penta-O-acetyl-D-myo-inositol D-7 and the corresponding L-isomer L-7. (2) Condensation of D-7 and L-7 with the glycosyl donor 3,4,6-tri-O-acetyl-2-deoxy-2-(2,4-dinitrophenylamino)-alpha-D-glucopyranosylbromide afforded the corresponding alpha and beta anomeric products, which could be resolved by silica gel chromatography. (3) Deprotection of these by hydrolysis using an anion exchange resin gave 1D- and 1L-1-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol 13 and 15 and the corresponding beta-coupled anomers 14 and 16. Only 13, and to a much lesser extent 15, were used by enzymes present in an ammonium sulphate fraction of a cellfree extract of Mycobacterium smegmatis for the enzymatic synthesis of mycothiol. In the absence of acetyl-SCoA, the immediate biosynthetic precursor of 1, desacetylmycothiol, was the major product.

Conjugates of plumbagin and phenyl-2-amino-1-thioglucoside inhibit MshB, a deacetylase involved in the biosynthesis of mycothiol

N-Acetylglucosaminylinositol (GlcNAc-Ins)-deacetylase (MshB) and mycothiol-S-conjugate amidase (Mca), structurally related amidases present in mycobacteria and other Actinomycetes, are involved in the biosynthesis of mycothiol and in the detoxification of xenobiotics as their mycothiol-S-conjugates, respectively. With substrate analogs of GlcNAc-Ins, MshB showed a marked preference for inositol as the aglycon present in GlcNAc-Ins. The inhibition of MshB and Mca by 10 thioglycosides, 7 cyclohexyl-2-deoxy-2-C-alkylglucosides, and 4 redox cyclers was evaluated. The latter contained plumbagin tethered via 2 to 5 methylene carbons and an amide linkage to phenyl-2-deoxy-2-amino-1-thio-alpha-d-glucopyranoside. These proved to be the most potent amongst the 21 compounds tested as inhibitors of MshB. Their inhibitory potency varied with the length of the spacer, with the compound with longest spacer being the most effective.

The use of ultrastable Y zeolites in the Ferrier rearrangement of acetylated and benzylated glycals

The Ferrier rearrangement of a selection of protected glycals was successfully performed using a commercially available H-USY zeolite CBV-720 as catalyst, selected after screening a range of similar catalysts. By incorporating either alcohols, thiophenol, trimethylsilyl azide or allyltrimethylsilane in the reaction it was shown that a range of O-, S-, N- and C-glycosides could be formed. With benzylated glucal and galactal in particular, use of the CBV-720 catalyst led to significantly higher yields of the 2,3-dehydroglycosides than previously reported.

A New Procedure for Highly Regio‐ and Stereoselective Iodoacetoxylation of Protected Glycals and α‐1,2‐Cyclopropanated Sugars

Protected glycals and α‐1,2‐cyclopropanated sugars were converted in high yields and selectivities in less than 2 h at low temperatures to 2‐deoxy‐2‐iodoglycosyl acetates or novel 2‐deoxy‐2‐iodomethylglycosyl acetates using the simple, inexpensive reagent mixture of ammonium iodide, hydrogen peroxide, and acetic anhydride/acetic acid in acetonitrile. The protected glycals gave rise to 2‐deoxy‐2‐bromoglycosyl acetates when ammonium bromide was used instead of the iodide, although longer reaction times were required and selectivities were inferior. Other simple olefins such as styrene and indene were also converted to their corresponding 1,2‐trans‐iodoacetates.

Synthesis of structures corresponding to the capsular polysaccharide of Neisseria meningitidis group A.

Four differently substituted trimers of the CPS repeating unit have been synthesised in order to investigate the dependence on oligosaccharide size, acetylation and mode of phosphorylation of glycoconjugate vaccines against Neisseria meningitidis group A. A spacer-containing starting monomer, a H-phosphonate elongating monomer and a 6-O-phosphorylated H-phosphonate cap monomer have been synthesised and coupled together to afford, after deprotection, the target trimer structures differing in their acetylation and phosphorylation substitution pattern.

Synthesis of 1,2,3,4‐tetrahydrocarbazole over zeolite catalysts

Abstract1,2,3,4‐tetrahydrocarbazole (CAR) has been synthesized over H‐ZSM‐12, H‐beta, H‐mordenite, H‐Y, H‐ZSM‐22, H‐EU‐1, H‐ZSM‐5 and acetic acid by Fishers method using phenylhydrazine and cyclohexanone. H‐Y is more active than the other zeolites studied for the synthesis of CAR. The influence of different parameters such as the duration of the run, catalyst concentration, reaction temperature and molar ratios of the reactants in the synthesis of CAR are also studied. A number of arylhydrazines such as o-tolylhydrazine, p-tolylhydrazine and 1,1‐diphenylhydrazine and cyclic ketones such as cyclopentanone, cyclohexanone and 3‐methylcyclohexanone have also been taken to study the effect of substitution in phenylhydrazine and the size of the cyclic ketones in the reaction. The yields of indoles correlated with the degree of substitution of the reactants and products, and the limitations imposed on diffusion through zeolite pores.