Isolation of novel anti-TB cyclohexapeptides from actinomycetes

G Cai; JG Napolitano; J McAlpine; S Cho; Y Wang; BU Jaki; JW Suh; SH Yang; IA Lee; GF Pauli; SG Franzblau

doi:10.1055/s-0032-1320753

Isolation of novel anti-TB cyclohexapeptides from actinomycetes

G Cai ¹^,², JG Napolitano ², J McAlpine ², S Cho ¹, Y Wang ¹, BU Jaki ¹^,², JW Suh ³, SH Yang ³, IA Lee ³, GF Pauli ¹^,², SG Franzblau ¹^,²

¹Institute for Tuberculosis Research
²Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, 833 S Wood St, Chicago, IL 60612, USA
³Center for Nutraceutical and Pharmaceutical Materials, Myongji University, Cheoin-gu, Yongin, Gyeonggi-Do 449–728, Korea

Abstract

Thirty-five thousand actinomycete extracts were screened for anti-TB activity, followed by C₁₈ cartridge fractionation of 37 prioritized extracts. Based on MICs against replicating and non-replicating M. tuberculosis (Mtb), and IC₅₀s against Vero cells to generate selectivity indices, seven fractions were selected for further separation. ECUM14046, a Streptomyces hygroscopicus strain, when cultured in GSS media and extracted with ethyl acetate, yielded a fraction with potent anti-TB activity. This fraction had a well-defined thin layer chromatography (TLC) profile and was therefore further fractionated using preparative HPLC. The molecular formulas of two purified components, designated as hytramycin-V and hytramycin-I, were determined by high-resolution mass spectrometry (ESI-IT-TOF) as C₃₀H₅₁N₉O₆ and C₃₁H₅₃N₉O₆, resp. Structure elucidation by 1D/2D NMR revealed both to be cyclohexapeptides with three unusual piperazic acid moieties. The MICs against replicating and especially non-replicating Mtb fall into the range of existing anti-TB drugs, such as streptomycin and capreomycin, and were maintained against Mtb strains that represent the major global clades, as well as H₃₇Rv-isogenic strains that are resistant to individual clinical anti-TB drugs.