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.

The discovery of capsazepine, the first competitive antagonist of the sensory neuron excitants capsaicin and resiniferatoxin.

Capsaicin and resiniferatoxin are natural products which act specifically on a subset of primary afferent sensory neurons to open a novel cation-selective ion channel in the plasma membrane. These sensory neurons are involved in nociception, and so, these agents are targets for the design of a novel class of analgesics. Although synthetic agonists at the capsaicin receptor have been described previously, competitive antagonists at this receptor would be interesting and novel pharmacological agents.

The 3D structure of a cyclosporin analogue in water is nearly identical to the cyclophilin-bound cyclosporin conformation.

The conformation of [D-MeSer3-D-Ser-(O-Gly)8]CS, a water soluble cyclosporin derivative, has been determined in (D6)DMSO and in water using NMR. In these polar solvents the conformation is identical and very similar to the structure found in the cyclophilin-cyclosporin complex. However, it differs significantly from its conformation in deuterated chloroform.

1H NMR studies of echistatin in solution. Sequential resonance assignments and secondary structure.

Two-dimensional 1H-NMR methods have been used to obtain complete proton resonance assignments for the 49-residue protein echistatin from the viper Echis carinatus. The protein in solution contains only a small amount of regular secondary structure with four very short beta-strands. These beta-strands form two short segments of antiparallel beta-sheet, as evidenced by the observed cross-strand NOE.