The variability of natural compound

The variability of natural compounds with t-butyl group can be illustrated (Fig. 1) by, e.g., pivalic acid or the nonproteinogenic amino acid tert-leucine (Tle). This amino acid was identified, for instance, in teleocidin derivatives, i.e., in blastmycetin E which is produced by the actinomycete Streptoverticillium blast-myceticum (Irie et al. 1990) or in bottromycin A, an antibiotic produced by Streptomyces bottropensis whose structure has been revised at least three times (Gouda et al. 2012). A considerable amount of the pivalic acid, which is found in nature, is assumed to be of anthropogenic origin, e.g., arriving from prodrugs (Brass 2002).