Rare Streptomyces N-Formyl Amino-salicylamides Inhibit Oncogenic K-Ras

During a search for inhibitors of oncogenic K-Ras, we detected two known and two new examples of the rare neoantimycin structure class from a liquid cultivation of Streptomyces orinoci, and reassigned/assigned structures to all based on detailed spectroscopic analysis and microscale C3 Marfey's and C3 Mosher chemical degradation/derivatization/analysis. SAR investigations inclusive of the biosynthetically related antimycins and respirantin, and synthetic benzoxazolone, documented a unique N-formyl amino-salicylamide pharmacophore as a potent inhibitor of oncogenic K-Ras.