Quality control in combinatorial chemistry: determinations of amounts and comparison of the "purity" of LC-MS-purified samples by NMR, LC-UV and CLND.

The absolute purities of 20 purified samples from a combinatorial library have been determined by a new method that uses the DMSO sidebands [1J[13C-1H]] as an internal standard for quantification. The obtained absolute amounts are compared with the amounts of sample obtained by weighing, with the calculated weights obtained by chemiluminescent nitrogen detection (CLND) chromatography and with the relative purities obtained by LC-UV chromatography.

Argyrins, immunosuppressive cyclic peptides from myxobacteria. II. Structure elucidation and stereochemistry.

The structures of argyrins A-H were elucidated by NMR spectroscopy, chemical degradation and X-ray analysis as cyclic octapeptides. Argyrins A and B, in addition to the common amino acids tryptophan, glycine, dehydroalanine and alanine or alpha-aminobutyric acid, sarcosine, contain 2-(1-aminoethyl)thiazol-4-caboxylic acid and the novel amino acid 4'-methoxytryptophan. In argyrins C and D the latter is replaced by 4'-methoxy 2'-methyltryptophan. According to NMR analysis the solution and crystal conformations of argyrins A and B are identical in CDCl3 and slightly different in acetone-d6. Argyrins A and B are identical with the antibiotics A21459 A and B, whose structures are revised with respect to 4'-methoxytryptophan.