18O/16O-Encoding Strategy for Microscale Stereochemical Determination of Peptidic Natural Products

The demand for more efficient methods of establishing the undetermined stereochemistries of peptidic natural products continues unabated. A new method for microscale stereochemical determination was devised by integrating solid-phase synthesis, split-and-mix randomization, O-18/O-16-encoding of d/l-configurations, tandem mass spectrometry, and biological evaluation. Here we applied gramicidin A as the molecule for a blind test. Gramicidin A and its 31 diastereomers were randomly prepared in microgram scale with O-18/O-16-stereochemical encoding and subjected to MS/MS-structural determination and cytotoxicity assay. Only the parent gramicidin A was selected from among the 32 stereoisomers, validating the high reliability of the present strategy.

Automated summary

A new method for microscale stereochemical determination of peptidic natural products was developed and tested using gramicidin A as a blind test molecule. The high reliability of the strategy was confirmed by successfully selecting the parent gramicidin A from among 32 stereoisomers.