Absolute configuration of the long chain B-amino acid obtained from the hydrolysate of iturin A has been determined to be R by application of Dnp-aromatic rule. This is the first assignment for the chirality of an iturinic acid.
Recently, Kawai and Nagai reported that Dnp-aromatic rule 1) can be used for determining the absolute configuration of aliphatic o-amino acids by deriving them to the N-2,4_dinitrophenyl-2) p-methoxyanilides (=Dnp-pMA) . The method is applicable also to amino acids having the amino group at other positions than a 3) . Because the CD spectra of N-Dnp-aminoacyl-pMA have their origin in interaction of the Dnp and the pMA groups, and insertion of a few methylene groups between them does not alter the nature of the interaction significantly, as exemplified in the case of Dnp-Phe homologs 1) .
In 1965, Delcambe reported the isolation of a lipophilic antifungal peptide, iturin, produced by Bacillus subtiZ.is 4) . Peypoux et al. purified the antibiotic, found new B-amino acids as its components, and elucidated the structure 5) . They were isolated as a mixture of two compounds having the structures, I and II. But, the stereochemistry remained undetermined.