Biosynthesis of thiopeptide antibiotic A10255: incorporation of isotopically-labeled precursors.

The biosynthetic origin of antibiotic A10255 was investigated using 14C- and 13C-labeled amino acids. DL-[1-(13)C]Serine labeled 15 of the 17 amino acid residues present in A10255G. These included the oxazole, thiazole, dehydroalanine, masked glycine, masked alanine and pyridine moieties. The same 15 residues labeled by serine were labeled by [2-(13)C]glycine, apparently by conversion of the glycine to [2,3-(13)C]serine. Formation of the pyridine ring occurred via a C3 to C3 condensation of two serines. The results indicated origin of the masked alanine from alanine; the masked glycine from glycine; the thiazole residues from cysteine; and the threonine, masked dehydrobutyrine, masked dehydronorvaline and masked dehydroleucine residues from threonine. L(-)[CH3-(13)C]Methionine labeled the methyl carbon of the masked dehydronorvaline moiety in factor B and the two methyl carbons of the masked dehydroleucine moiety in factor E. The results demonstrate that A10255 originates exclusively from amino acids in a manner similar to the closely related thiopeptide antibiotics nosiheptide and thiostrepton.

Bipyridine cardiotonics: the three-dimensional structures of amrinone and milrinone.

The cardiotonic drug milrinone (1,6-dihydro-2-methyl-6-oxo-[3,4'-bipyridine]-5-carbonitrile) is superior to its analogue amrinone (5-amino-[3,4'-bipyridin]-6(1H)-one) by virtue of its greater potency and reduced side effect profile. We confirmed initial reports on the potencies of milrinone and amrinone and found that after intravenous administration to phenobarbital anesthetized dogs, the drugs had cumulative inotropic ED50's of 37 and 1891 micrograms/kg, respectively; relative effects on heart rate and blood pressure were comparable. There are two structural differences between amrinone and milrinone: (1) milrinone has a pyridone 2-methyl substituent and (2) the pyridone 5-amino substituent of amrinone is replaced with a nitrile in milrinone. We confirmed structure-activity studies that indicated that the 2-methyl substituent appears to be primarily responsible for the dramatic difference in the potencies of amrinone and milrinone. A plausible explanation for the effect of the methyl substituent is an altered molecular topology resulting from its steric interaction with the 3',5'-hydrogen atoms. Consequently, we probed the three-dimensional structures of these two compounds by X-ray crystallography. The dihedral angle between the planes formed by the two aromatic rings of amrinone was 1.3 degrees. In marked contrast, the corresponding angle for milrinone was 52.2 degrees. Moreover, 1H NMR studies revealed conformational differences in solution. Whereas the 2-methyl substituent undoubtedly produces some electronic and hydrophobic perturbations in the bipyridine cardiotonic series, the most significant effect, from a global viewpoint, is the altered molecular topology.

High performance liquid chromatography (HPLC) of natural products. IV. The use of HPLC in biosynthetic studies of cephalosporin C in the cell-free system.

A new cepham metabolite has been isolated from the filtered broth of Cephalosporium acremonium by high performance liquid chromatography (HPLC) and identified as 7 beta-(5-D-amino-adipamido)-3 beta-hydroxy-3 alpha-methyl-cepham-4 alpha-carboxylic acid (I). Pure penicillin N was prepared using HPLC in the analytical mode. When I was added in place of penicillin N as substrate for the cell-free biosynthetic of cephalosporin, no formation of deacetoxycephalosporin C (II) was observed. A synthetic cepham derivative, 7 beta-(5-D-aminoadipamido)-3-exomethylene-cepham-4 alpha-carboxylic acid (III) was also tested in the cell-free system as a possible intermediate. The compound III was shown to be an inhibitor of the ring expansion enzyme that converts penicillin N to deacetoxycephalosporin C.