Co(III)-Catalyzed C─H Amidation of Dehydroalanine for the Site-Selective Structural Diversification of Thiostrepton

Thiostrepton is a potent antibiotic against a broad range of Gram-positive bacteria, but its medical applications have been limited by its poor aqueous solubility. In this work, the first C(sp 2 )─H amidation of dehydroalanine (Dha) residues was applied to the site selective modification of thiostrepton to prepare a variety of derivatives. Unlike all prior methods for the modification of thiostrepton, the alkene framework of the Dha residue is preserved and with complete selectivity for the Z-stereoisomer. Additionally, an aldehyde group was introduced by C─H amidation, enabling oxime ligation for the installation of an even greater range of functionality. The thiostrepton derivatives generally maintain antimicrobial activity, and importantly, eight of the derivatives displayed improved aqueous solubility (up to 28-fold), thereby addressing a key shortcoming of this antibiotic. The exceptional functional group compatibility and site selectivity of Co(III)-catalyzed C(sp 2 )─H Dha amidation suggests that this approach could be generalized to other natural products and biopolymers containing Dha residues. Co(III)-catalyzed C─H amidation was used for the site-selective modification of the antibiotic thiostrepton. A range of amide groups was installed with 1,4,2-dioxazolone coupling partners. The introduction of an aldehyde group by C─H amidation enabled modular incorporation of additional functionality by oxime formation. A number of the thiostrepton derivatives showed greatly improved aqueous solubility while maintaining antibacterial activity.