Synthesis, Chemical, and Biological Evaluation of Actinomycin Tetracyclic Oxazinone Derivatives and Application to Small-Molecule Drug Conjugates

Abstract Actinomycin D (1) is a chromopeptide antibiotic natural product used in the treatment of various malignancies, although its clinical use is limited by high toxicity. Tetracyclic actinomycin oxazinone derivatives have been reported to generate 1 through hydrolysis under physiological conditions, but detailed mechanistic studies of this process have remained limited. Herein, we synthesized a series of oxazinone derivatives using α-keto esters and systematically investigated their hydrolytic behavior. LC-MS monitoring, substituent-dependent kinetic studies, Hammett analysis, and crossover experiments provided insight into the hydrolysis process and the formation of oxazole-containing by-products. The chemical and biological properties of the synthesized derivatives were investigated. In addition, actinomycin-based small-molecule drug conjugates (SMDCs) were synthesized.