13C nuclear magnetic resonance spectra of diastereomeric C-24 alkyl sterols have been assigned. Differences in the chemical shifts of side-chain carbons permitted the determination of the absolute configuration at C-24 in several sterols since these chemical shifts are insensitive to structural changes remote from the asymmetric centre. An unknown sterol from Tetraselmissuecica has been identified as (24R)-24-methylcholest-5-en-3β-ol and the configuration assigned from 1H nmr data to the sterol from Phaeodoctylumtricornutum has been confirmed. The utility and potential of this method in characterising new sterols and their biological precursors is discussed.

Tenellin and bassianin are deduced from chemical and spectroscopic evidence to be the 3-[(E,E)-4,6-dimethylocta-2,4-dienoyl] and 3-[(E,E,E)-6,8-dimethyldeca-2,4,6-trienoyl] derivatives of 1,4-dihydroxy-5-(p-hydroxyphenyl)-2(1H)-pyridone. Spin–spin coupling information in the 1H and 13C nuclear magnetic resonance spectra after biosynthetic enrichment of tenellin with 13C and 15N isotopes was a valuable aid in elucidating the structure.

1% n.m.r. spectroscopy was used for the dual alanine, and methionine; precursors in which two adjacent sites are labelled can provide superior information, and may prove useful for obtaining enrichment data at low incorporations. purpose of assessing the relative merits of singly and doubly labelled precursors while establishing the biosynthesis of tenellin from 13C-labelled acetate, phenyl-

Oxidation with permanganate of caerulomycin A labeled biosynthetically from [U-14C]lysine in cultures of Streptomyces caeruleus yielded picolinic acid with the same specific activity as the antibiotic. [3H]Picolinic acid was incorporated into caerulomycin A with high efficiency and the label was also found exclusively in picolinic acid after oxidation, implicating free picolinic acid as an intermediate in the pathway from lysine. The substituted pyridyl ring of caerulomycin was labeled by [2-13C, 1,3-14C]glycerol. 13C nuclear magnetic resonance analysis located the 13C predominantly at C-6, suggesting that C-5, C-6, and C-7 were derived from glycerol as an intact three-carbon precursor. Since no incorporation of [1-13C]glyceric acid was detected and [3-13C, 3-14C]methylglyoxal labeled the antibiotic only marginally, these compounds are probably not biosynthetic intermediates en route from glycerol. A new caerulomycin possessing an aldehyde in place of the aldoxime substituent at C-6 was isolated from culture broths and is postulated to be a late intermediate in the formation of caerulomycin A.

. Can. J Chem. 56, 11 55 (1978). Resonances in the 13C nmr spectra of nonylprodiginine, cyclononylprodiginine, methylcyclodecylprodiginine, and butylcycloheptylprodiginine were assigned using information from the literature, from high resolution spectra and double irradiation experiments, and from ' 3 C -1 5 N~~~p l i n g~ observed in samples of nonylprodiginine enriched with I5N. Supplementation of cultures with sodium [I-13C]-and [1,2-13C]acetate gave I3C-enriched prodiginines and the labeling patterns were established from 13C nmr spectra. These indicated that rings A and B were formed in a similar manner to rings A and B in prodigiosin and other prodiginine pigments. Ring C and ihe C2-alkyl substituent were derived in part from acetate units that were condensed in a linear 12-or 14-carbon chain. The same pattern of acetate assembly has been found in all actinomycete prodiginines examined.