Laird A. Trimble

An acid metabolite of cyclosporine

The primary biliary metabolite of cyclosporine has been isolated from rabbit and human bile. The material has been identified by mass spectrometry and by nuclear magnetic resonance spectrometry as an acidic metabolite of cyclosporine in which the eta-methyl group of the cyclosporine-specific nine carbon amino acid #1 has been oxidized to an alpha, beta unsaturated carboxylic acid functionality. This major cyclosporine metabolite is inactive in a phytohemagglutinin stimulated lymphocyte proliferation assay.

Application of stable isotope labelling methodology to the biosynthesis of the mycotoxin, terretonin, by aspergillus terreus: incorporation of 13C-labelled acetates and methionine, 2H- and 13C, 18O-labelled ethyl 3,5-dimethylorsellinate and oxygen-18 gas

Abstract Incorporation of 13C-labelled acetates and methionine, 14C and 2H-labelled ethyl 3,5-dimethylorsellinate into terretonin (5) by cultures of Aspergillus terreus indicated that its biosynthesis proceeds via a mixed polyketide-terpenoid (meroterpenoid) pathway. Incorporation of 18O2 gas and ethyl 3,5-dimethylorsellinate (7) doubly labelled with 13C and 18O in the carbonyl of the carboxyl group and at the C-6 position into terretonin (5) and observation of 18O isotope-induced shifts in the 13C n.m.r. spectra and GC/MS studies of the enriched metabolites determined the origin of all of the oxygen atoms in (5) and provided mechanistic insight into the biosynthetic pathway.

Studies on the biosynthesis of the mycotoxin austin, a meroterpenoid metabolite of Aspergillus ustus

Incorporations of 13C-labelled acetates and methionine into the mycotoxin austin in cultures of Aspergillus ustus give a labelling pattern consistent with a mixed polyketide-terpenoid pathway. Incorporations of 14C and 2H labelled 3,5-dimethylorsellinate confirm the intermediary of a preformed tetraketide-derived phenolic precursor. Further information on the mechanisms involved in the modifications of both the farnesyl- and tetraketide-derived portions of the molecule are provided by incorporation studies with [1-13C,18O2]acetate, [methyl-13C,2H3] methionine, 13C,18O-labelled dimethylorsellinate,18O2 gas and [6-13C,6-2H3]mevalonic acid lactone.

Biosynthesis of tajixanthone and shamixanthone by Aspergillus variecolor: incorporation of oxygen-18 gas

Mass spectral and 13C n.m.r. analyses of tajixanthone (1) and shamixanthone (2) formed during growth of Aspergillus variecolor under atmospheres containing [18O2] oxygen gas showed incorporation of four and three 18O labels per molecule of (1) and (2), respectively, and provided information about the mode of xanthone ring formation.

Biosynthesis of the meroterpenoid austin, by Aspergillus ustus: synthesis and incorporation of 13C,18O-labelled ethyl 3,5-dimethylorsellinate

Ethyl 3,5-dimethylorsellinate (3) doubly labelled with 13C and 18O in the carbonyl of the carboxy group and at the C-6 position has been synthesised using a four-step procedure from sodium [1-13C, 18O2]acetate, and incorporated into austin (1) by cultures of Aspergillus ustus.

Biosynthesis of the meroterpenoid metabolite, andilesin A, by Aspergillus variecolor: origins of the oxygen atoms

The origins of all the oxygen atoms in andilesin A (1) have been determined by labelling studies with [1-13C, 18O2]acetate, 18O2, and ethyl 3,5-dimethylorsellinate doubly-labelled with 13C and 18O at the carbonyl group and at C-6; the results suggest a biosynthetic pathway in which andilesin A(1) is dehydrated to give andilesin B (2) which is then reduced to andilesin C (3).

Biosynthesis of aspyrone and asperlactone, pentaketide metabolites of Aspergillus melleus. Incorporation studies with [1-13C, 18O2]acetate and 18O2 gas

Incorporation of [1-13C,18O2] acetate and 18O2 gas into aspyrone (1) and asperlactone (2) by cultures of Aspergillus melleus and observation of 18O isotope-induced shifts in the 13C n.m.r. spectra of the enriched metabolites establish the origins of all the oxygen atoms and suggest a biosynthetic pathway involving epoxide-mediated rearrangement and ring closure reactions.

Biosynthesis of monocerin. Incorporation of 2H-, 13C-, and 18O-labelled acetates by Drechslera ravenelii

Incorporation of 2H-, 13C-, 18O-labelled acetates into monocerin (1) by cultures of Drechslera revenelii and analysis of the enriched metabolites by 2H and 13C n.m.r. spectroscopy indicate a heptaketide origin; observation of 2H and 18O isotope shifts in the 13C n.m.r. spectrum allows the fate of acetate-drived hydrogen and oxygen on incorporation into monocerin to be followed and conclusions on the mechanism of formation of the fused furobenzopyrone ring system to be drawn.

Biosynthesis of LL-D253α in Phoma pigmentivora. Incorporation of 13C, 2H, and 18O enriched precursors

The incorporation of 13C, 2H, and 18O labelled acetates and 18O2 gas into LL-D253α(1), a chromanone metabolite of Phoma pigmentivora, and analyses of the enriched metabolites by 13C and 2H n.m.r. and mass spectroscopy indicate its formation from two preformed polyketide chains; evidence for the mechanism of formation of the chromanone ring is presented, and a cyclopropyl intermediate is proposed to account to account for the unique randomisation of label observed in the hydroxyethyl side chain.

Biosynthesis of the meroterpenoid, austin, by Aspergillus ustus: incorporation of 18O2, sodium [1-13C, 18O2]acetate, and [Me-13C, 2H3]methionine

Mass spectral and 13C n.m.r. analyses of austin (1) produced by fermentation of Aspergillus ustus in the presence of 18O2 and [Me-13C,2H3]methionine showed that all labelled methionine-derived hydrogens were retained, determined that five of nine oxygens were introduced by aerobic oxidation, and elucidated the general mechanism of late biosynthetic stages.