Tetrachloromaxamycins: Divergent Total Synthesis and Initial Assessments.

Abstract

Divergent total syntheses of binding pocket and peripherally modified tetrachlorovancomycins, a non-native synthetic glycopeptide, and their evaluation are disclosed. Central to the approach is the synthesis of a single late-stage intermediate that bears a residue 4 thioamide ([Ψ[C(═S)NH]Tpg4]tetrachlorovancomycin (3), LLS 15 steps, 14% overall) as a precursor to either of two key pocket modifications and their pairing with any combination of two peripheral modifications conducted without protecting groups. A stereochemical simplification achieved by the addition of two aryl chlorides removes two synthetically challenging atropisomer centers in native glycopeptides and streamlines the synthesis. Key features include in a convergent epimerization-free thioacylation of the AB ring system amine with an N-thioacylbenzotriazolyl DE tetrapeptide (85%) followed by simultaneous room-temperature SNAr macrocyclizations of the CD and DE ring systems (96%). The approach provided 3 from which [Ψ[C(═N)NH]Tpg4]tetrachlorovancomycin (4) and [Ψ(CH2NH)Tpg4]tetrachlorovancomycin (5) were prepared in a single-step and bear binding pocket modifications that convey dual d-Ala-d-Ala/d-Lac ligand binding to overcome vancomycin resistance. The newest maxamycin members are disclosed, bearing two additional peripheral modifications that introduce two independent synergistic MOAs that do not rely on native ligand binding for activity. Ligand binding properties of pocket-modified tetrachlorovancomycins 3-5, antibacterial activity of a key compound series, and PK assessments of two tetrachloromaxamycins are reported.