nocathiacin-i and thiazomycin

Thiazolyl peptides are a class of natural products with potent Gram-positive antibacterial activities. Lack of aqueous solubility precluded this class of compounds from advancing to clinical evaluations. Nocathiacins and thiazomycins are sub-classes of thiazolyl peptides that are endowed with structural features amenable for chemical modifications. Semi-synthetic modifications of nocathiacin led to a series of analogs with improved water solubility, while retaining potency and antibacterial spectrum. We studied the activities of a selection of two natural products (nocathiacin and thiazomycin) as well as seven polar semi-synthetic analogs against twenty clinical strains of Mycobacterium tuberculosis with MDR phenotypes. Two compounds show useful activity against H37Rv strain with MIC values ⩽1 μM, two (⩽0.5 μm) and three (⩽10 μm). These two derivatives showed MIC values ⩽2.5 μm against most of the 20 MDR strains regardless their resistance profile. Specifically, these lack cross-resistance to rifampicin, isoniazid and moxifloxacin.

Topics: Antitubercular Agents; Drug Resistance, Multiple, Bacterial; Fluoroquinolones; Intercellular Signaling Peptides and Proteins; Isoniazid; Microbial Sensitivity Tests; Moxifloxacin; Mycobacterium tuberculosis; Peptides; Peptides, Cyclic; Rifampin; Solubility; Thiazoles

Thiazolyl peptides are a class of rigid macrocyclic compounds richly populated with thiazole rings. They are highly potent antibiotics but none have been advanced to clinic due to poor aqueous solubility. Recent progress in this field prompted a reinvestigation leading to the isolation of a new thiazolyl peptide, thiazomycin, a congener of nocathiacins. Thiazomycin possesses an oxazolidine ring as part of the amino-sugar moiety in contrast to the dimethyl amino group present in nocathiacin I. The presence of the oxazolidine ring provides additional opportunities for chemical modifications that are not possible with other nocathiacins. Thiazomycin is extremely potent against Gram-positive bacteria both in vitro and in vivo. The titer of thiazomycin in the fermentation broth was very low compared to the nocathiacins I and III. The lower titer together with its sandwiched order of elution presented significant challenges in large scale purification of thiazomycin. This problem was resolved by the development of an innovative preferential protonation based one- and/or two-step chromatographic method, which was used for pilot plant scale purifications of thiazomycin. The isolation and structure elucidation of thiazomycin is herein described.

Topics: Actinomycetales; Anti-Bacterial Agents; Chromatography, Liquid; Fermentation; Gram-Positive Bacteria; Intercellular Signaling Peptides and Proteins; Mutation; Peptides; Peptides, Cyclic; Solubility; Thiazoles