Stereospecific Biosynthesis of p-Methyltryptophan from L-Tryptophan Features a Stereochemical Switch

摘要

Nonproteinogenic amino acids, especially β-methyl amino acids, are important building blocks in the assembly of bioactive natural products. For example, β-methyl aspartic acid is a biosynthetic precursor of friulimicin, nikkomycin, streptolydigin, and vicenistatin, (25,35)-β-methylphenylalanine is a precursor of mannopeptimycin,161 and the lipopep-tide antibiotics daptomycin, calcium-dependent antibiotic (CDA), and A54145 contain a (2S,3R)-β-methyl glutamate unit. Intriguingly, two different diastereoisomers of β-methyl tryptophan (β-MeTrp) have been found to contribute to nonribosomally synthesized peptides and tryptophan-derived alkaloids: maremycin A and B (MARs) and FR900452 contain the (2S,3S)-β-MeTrp (5) unit, while chaetoglobisin K, indolmycin, and telo-mycin contain the (2S,3R)-β-MeTrp (4) moiety (Figure 1).