Genomic and Spectroscopic Signature-Based Discovery of Natural Macrolactams.

The logical and effective discovery of macrolactams, structurally unique natural molecules with diverse biological activities, has been limited by a lack of targeted search methods. Herein, a targeted discovery method for natural macrolactams was devised by coupling genomic signature-based PCR screening of a bacterial DNA library with spectroscopic signature-based early identification of macrolactams. DNA library screening facilitated the efficient selection of 43 potential macrolactam-producing strains (3.6% of 1,188 strains screened). The PCR amplicons of the amine-deprotecting enzyme-coding genes were analyzed to predict the macrolactam type (α-methyl, α-alkyl, or β-methyl) produced by the hit strains. H-N HSQC-TOCSY NMR analysis of N-labeled culture extracts enabled macrolactam detection and structural type assignment without any purification steps. This method identified a high-titer strain producing salinilactam (), a previously reported α-methyl macrolactam, and two strains producing new α-alkyl and β-methyl macrolactams. Subsequent purification and spectroscopic analysis led to the structural revision of and the discovery of muanlactam (), an α-alkyl macrolactam with diene amide and tetraene chromophores, and concolactam (), a β-methyl macrolactam with a [16,6,6]-tricyclic skeleton. Detailed genomic analysis of the strains producing - identified putative biosynthetic gene clusters and pathways. Compound displayed significant cytotoxicity against various cancer cell lines (IC = 1.58 μM against HCT116), whereas showed inhibitory activity against sortase A. This genomic and spectroscopic signature-based method provides an efficient search strategy for new natural macrolactams and will be generally applicable for the discovery of nitrogen-bearing natural products.