David F. Ewing

Accumulation of a poly(hydroxyalkanoate) copolymer containing primarily 3-hydroxyvalerate from simple carbohydrate substrates by Rhodococcus sp. NCIMB 40126☆

A number of taxonomically-related bacteria have been identified which accumulate poly(hydroxyalkanoate) (PHA) copolymers containing primarily 3-hydroxyvalerate (3HV) monomer units from a range of unrelated single carbon sources. One of these, Rhodococcus sp. NCIMB 40126, was further investigated and shown to produce a copolymer containing 75 mol% 3HV and 25 mol% 3-hydroxybutyrate (3HB) from glucose as sole carbon source. Polyesters containing both 3HV and 3HB monomer units, together with 4-hydroxybutyrate (4HB), 5-hydroxyvalerate (5HV) or 3-hydroxyhexanoate (3HHx), were also produced by this organism from certain accumulation substrates. With valeric acid as substrate, almost pure (99 mol% 3HV) poly(3-hydroxyvalerate) was produced. N.m.r. analysis confirmed the composition of these polyesters. The thermal properties and molecular weight of the copolymer produced from glucose were comparable to those of PHB produced by Alcaligenes eutrophus.

5-epi-aristolochene is a common precursor of the sesquiterpenoid phytoalexins capsidiol and debneyol

Abstract 5- epi -Aristolochene (4- epi -eremophila-9, 11-diene) has been identified (GC-MS and high-field 1 H NMR) as the hydrocarbon (unknown I ) which is accumulated when the formation of capsidiol and debneyol from [1- 3 H 2 ]FPP in cell-free preparations of cells from cellulase-elicited cell-suspension cultures of Nicotiana tabacum is inhibited by the omission of NADPH or the exclusion of molecular oxygen from the incubation mixture. Feeding experiments with 14 C-labelled 5- epi -aristolochene have shown this compound to be a common precursor of the two sesquiterpenoid phytoalexins capsidiol and debneyol which accumulate in the elicited cultures. The evidence suggests that the biosynthesis of capsidiol is regulated, in part, by the activity of the first of the two hydroxylases which catalyse its formation from this hydrocarbon and furthermore, that this 3-hydroxylase is induced during the elicitation process.

Determination of the structure of exochelin MN, the extracellular siderophore from Mycobacterium neoaurum

BACKGROUND Siderophores are compounds produced by bacteria to acquire iron. Exochelin MN, the extracellular siderophore from Mycobacterium neoaurum, is of particular interest because it has been shown to transport iron into M. leprae, which is responsible for the disease leprosy. Exochelins from other species cannot mediate iron transport in M. leprae, suggesting a specific uptake mechanism involving exochelin MN. We set out to determine the structure of exochelin MN and identify the features of the molecule that may account for this specificity. RESULTS The structure of exochelin MN was elucidated by a combination of techniques including nuclear magnetic resonance, mass spectrometry, derivatization and gas chromatography. Exochelin MN is a peptide, containing the unusual amino acid beta-hydroxyhistidine and an unusual N-methyl group. The peptide coordinates iron(III) octahedrally using its two cis-hydroxamate groups plus the hydroxyl and imidazole nitrogen of the beta-hydroxyhistidine. The three-dimensional structure of the hexadentate exochelin/gallium complex was deduced from NMR data. CONCLUSIONS Exochelin MN has some structural features in common with other siderophores, but has a unique three-dimensional structure, which is presumably important for its specific activity in M. leprae. Exochelin MN may be a target for drug design in the fight against infection with this pathogen.

Production of a co-polyester of 3-hydroxybutyric acid and 3-hydroxyvaleric acid from succinic acid by Rhodococcus ruber: biosynthetic considerations

The biosynthesis of the 3-hydroxyvalerate (3HV) monomer of polyhydroxyalkanoate by Rhodococcus ruber from succinic acid was investigated using nuclear magnetic resonance analysis. Polymer produced from [2,3-13C]- and [1,4-13C]succinate showed that the C-1-C-2 and C-4-C-5 fragments of 3HV were derived from carbons 2 and 3 of succinate, essentially without bond cleavage, and carbon 3 of 3HV was derived from a carboxyl carbon of succinate. Using [1,2-13C]succinate it was demonstrated that the C-1-C-2 bond of succinate was cleaved during polymer biosynthesis. Methylmalonyl-coenzyme A (CoA) mutase activity was detected in cell-free extracts of R. ruber by enzyme assay and HPLC analysis of reaction products. A pathway, involving the known methylmalonyl-CoA pathway for propionate formation in Propionibacteria, followed by the established pathway for PHA biosynthesis from propionyl-CoA and acetyl-CoA, is proposed for the biosynthesis of 3HV from succinate by R. ruber.

Nucleoside Analogues with a Novel Glycone Based on the Benzo[C]Furan Core

Abstract Routes to novel nucleoside analogues based on 1, 3-dihydrobenzo[c]furan have been investigated. Thus l-(1, 3-dihydro-3-hydroxymethylbenzo[c]furan-1-yl)-thymine, an analogue of d4T, was obtained as two diastereoisomers. The cis compound (quasi β-D/α-L stereochemistry) was obtained pure but the trans compound was only 90% pure. A purine analogue with a four atom spacer group between base and glycone was also prepared. The conformation of these constrained nucleosides was studied by molecular modelling.

Sesquiterpenoids related to the phytoalexin debneyol from elicited cell suspension cultures of Nicotiana tabacum

Abstract Three new sesquiterpenoids, 7- epi -debneyol, 1-hydroxydebneyol and 8-hydroxydebneyol have been isolated, along with the phytoalexins capsidiol and debneyol, from cellulase-treated cell suspension cultures of Nicotiana tabacum . The identity of the new compounds was confirmed by 1 H NMR analysis of a series of chemical derivatives and by chemical means. It is proposed that the hydrocarbon 4- epi -eremophila-9,11-diene is a common intermediate in the biosynthesis of all the named compounds and further that 8-hydroxydebneyol is the direct precursor of the phytoalexin cyclodebneyol.

The effect of hydrogen bonding, molecular shape, dipole moments, and chain length on the mesomorphism of some D-glucose and D-glucosamine derivatives

Diverse 4-substituted-benzyl 1-O-alpha- and beta-D-glucopyranosides, 4-substituted-benzyl 2-deoxy2-trifluoroacetamido-alpha- and beta-D-glucopyranosides and 4-substituted-benzyl 2-acetamido2-deoxy-alpha- and beta-D-glucopyranosides have been synthesized. They were prepared directly by a one-step alkylation of commercially available carbohydrate starting materials. The 4-substituted-benzyl 2-deoxy-2-trifluoroacetamido-alpha- and beta-D-glucopyranosides were cleaved to yield the corresponding free amines. The influence of hydrogen bonding, terminal dipole moments, molecular shape and chain length on the thermotropic mesomorphic behaviour of these benzyl-substituted carbohydrate amphiphiles is discussed. Comparisons between the mesomorphic behaviour of the new benzyl-substituted carbohydrates and that of the related phenyl-substituted carbohydrates, as well as the non-aromatic n-alkyl D-glucosides, are made. Although the new carbohydrates do not exhibit lyotropic phase behaviour, the 4-substitutedbenzyl 2-de...

Facile separation of chiral 1,3-dihydrobenzo[c]furan derivatives using a d-xylose moiety as a protecting group

Abstract 1,2-O-Isopropylidene-α- d -xylofuranose has been used to protect one aldehyde group of o-phthalaldehyde. This chiral protecting group acts as a resolving agent and this leads to separable diastereoisomers when a new stereogenic centre is created by the conversion of the second aldehyde group to a benzyloxyhydroxyethyl chain. These separated diastereoisomers were cyclised to 1,3-dihydrobenzo[c]furans with retention of chiral integrity at the C3 site thus allowing further elaboration to enantiomerically pure nucleoside analogues.

Antifungal compounds from immature avocado fruit peel

Abstract Three antifungal compounds isolated from the peel of immature Avocado fruit have been identified as 1,2,4-trihydroxyheptadec-16-yne, 1,2,4-trihydroxyheptadec-16-ene and 1 -acetoxy-2,4-dihydroxyheptadec-16-yne, previously detected in extracts from avocado seeds.

Derivatisation of 1,3,4,6-Tetra-O-Benzoyl-α-D-Fructofuranose at the Anomeric Site : O-Alkylation, O-Acylation, O-Arylation, Amination and Selenation Reactions

Abstract Treatment of D-fructose with benzoyl chloride gave either 1,2,3,4,6-penta-O-benzoyl-α-D-fructofuranose or 1,3,4,6-tetra-O-benzoyl-α-D-fructofuranose (lα) which with methanol, 2-nitrophenol, or 4-nitrophenol in the presence of the Mitsunobu reagents, diisopropyl azodicarboxylate and triphenylphosphine, gave the corresponding fructofuranosides in good yield; an analogous reaction with 4-methoxybenzylamine gave the corresponding D-fructo-furanosylamine. Alkylation with isopropyl alcohol or t-butyl alcohol was complicated by competition from transesterification and fructose disaccharide formation. There was little or no inversion in these reactions. The 2-O-acetyl derivative of 1 reacted with selenophenol and diethyl ether-boron trifluoride to give phenyl l-deoxy-3,4,6-tri-O-benzoyl-2-seleno-α,β-D-fructofuranose as a minor product and phenyl l,3,4,6-tetra-O-benzoyl-2-seleno-α,β-D-fructo-furanose which with tris(trimethylsilyl)silane and AIBN gave l,3,4,6-tetra-O-benzoyl-2,5-anhydro-D-mannitol and l,3...