Discovery, Design, and Synthesis of Novel 2‑Benzyl-2,7-diazaspiro[3.5]nonane Benzothiazinones with Broad-Spectrum Antimycobacterial Activity

Despite
their nanomolar potency against M. tuberculosis (MTB), benzothiazinone (BTZs) DprE1 inhibitors like PBTZ169 are
ineffective against nontuberculous mycobacteria (NTM) due to a Cys387Ala
mutation in the NTM DprE1 target. Here, 529 BTZs in our lab were screened
againstM. abscessus, and two hits with
the 2-benzyl-2,7-diazaspiro[3.5]nonane scaffold showed enhanced activity.
Subsequent optimization led to the discovery of lead compound B2 with potent activity against MTB (MIC: < 0.01 μg/mL)
and NTM strains (MIC: < 0.03125–2.5 μg/mL). Notably, B2 also has good safety and oral pharmacokinetic (PK) profiles.
Further chiral resolution revealed its R-enantiomer (B2-1) as a more active form. Mechanistic investigations showed that B2-1 establishes a stable electrostatic interaction with Asp326
ofM. abscessusDprE1. As this residue
is highly conserved among mycobacterial species, such an interaction
likely underpins its broad-spectrum activity. Therefore, our findings
provide a blueprint for developing next-generation BTZs with broad-spectrum
activity against mycobacteria.