Identification of a new series of benzothiazinone derivatives with excellent antitubercular activity and improved pharmacokinetic profiles

Abstract

Nitrobenzothiazinone (BTZ) is a promising scaffold with potent activity against M. tuberculosis by inhibiting decaprenylphosphoryl-beta-d-ribose 2'-oxidase (DprE1). But unfavorable durability poses a challenge to further development of this class of agents. Herein, a series of BTZs bearing a variety of different substituents at the C-2 position were designed and synthesized. Compounds were screened for their antimycobacterial activity against Mycobacterium tuberculosis H37Ra and were profiled for metabolic stability, plasma protein-binding capacity and pharmacokinetics in vivo. In general, these new BTZs containing N-piperazine, N-piperidine or N-piperidone moiety have excellent antitubercular activity and low cytotoxicity. Several of the compounds showed improved microsomal stability and lower plasma protein-binding, opening a new direction for further lead optimization. And we obtained compound 3o, which maintained good anti-tuberculosis activity (MIC = 8 nM) and presented better in vitro ADME/T and in vivo pharmacokinetic profiles than reported BTZ compound PBTZ169, which may serve as a candidate for the treatment of tuberculosis.

Fig. 1. (a) BTZ043 (b) PBTZ169 (c) hit compound M-1.

Scheme 1. Synthesis of nitrobenzothiazinone derivative: (a) cat. DMF, oxalyl chloride, DCM, rt; (b) cat. 18-crown-6, NH₄SCN, DCM, rt; (c) tert-butyl piperazine-1-carboxylate, DCM, rt; (d) cat. TFA, DCM, rt; (h) cat. K₂CO₃, ester, dry DMF, 60 °C, 3 h; (e) 1a5-1d5, DCM, rt; (f) DCM, rt. (g) cat. K₂CO₃, ester, dry DMF, 60 °C 3 h.

Scheme 2. Synthesis of amine derivatives: (h) cat. EDCI, HOBT, Boc-glycine, DCM, rt.12 h; (i) cat. TFA, DCM, rt, 1 h; (j) cat. TEA, 4-nitrobenzenesulfonyl chloride, 0 °C, 0.5 h, rt, 6 h; (k) cat. K₂CO₃, 1,2-dibromoethane, DMF, 60 °C; (l) cat. LiOH, methyl-mercaptopropionat, CAN/DMSO (v/v = 49/1), 50 °C, 6 h; (m) cat. TEA, DCM, rt; (n) cat. TFA, DCM, 0 °C, 0.5 h, rt, 1.5–4 h; reagents and conditions: (o) cat. PPh3, DEAD, THF, rt; (p) cat. TFA, DCM, rt; (q) cat. NaH, dry DMSO, rt, 0 °C, 0.5 h, rt; (r) cat. NaH, dry DMF, 0 °C, 0.5 h, rt.

Fig. 2. (a) Mean plasma concentration–time profiles of 3o after IV and PO dose in ICR mice (n = 3) (mean ± sd). (b) Mean lung concentration–time profiles of 3o after IV and PO dose in ICR mice (n = 3) (mean ± sd). (c) Mean plasma concentration–time profiles of PBTZ169 after IV and PO dose in ICR mice (n = 3) (mean ± sd). (d) Mean lung concentration–time profiles of PBTZ169 after IV and PO dose in ICR mice (n = 3) (mean ± sd).