Design, Synthesis, and Biological Evaluation of β-Ketosulfonamide Adenylation Inhibitors as Potential Antitubercular Agents

Abstract

The antitubercular nucleoside antibiotics 1 and 2 were recently described that inhibit the adenylateforming enzyme MbtA and disrupt biosynthesis of the virulence-conferring siderophore known as mycobactin in M. tuberculosis. Herein, we report efforts to refine this inhibitor scaffold by replacing the labile acylsulfamate linkage (highlighted) with the more chemically robust β-ketosulfonamide linkage of 3 and 4.Mycobacterium tuberuculosis, the etiological agent of tuberculosis (TB), is the leading bacterial cause of infectious disease mortality. 1 The development of M. tuberculosis strains which are resistant to all of the current front-line antitubercular drugs has prompted worldwide efforts to discover new antibiotics to treat this notorious pathogen. Iron acquisition is an essential process for M. tuberculosis as well as almost all other microorganisms. 2 However, this essential micronutrient is highly sequestered in a mammalian host. Bacteria have evolved a variety of mechanisms to obtain this vital nutrient, but the most common mechanism involves the synthesis of small-molecule iron chelators, termed siderophores. 3 M. tuberculosis produces a pair of related peptidic siderophores known as mycobactin-T 8 and carboxymycobactins 9 that vary by the appended lipid residue and will hereafter be refered to collectively as the mycobactins (Figure 1). 4 The critical role of the mycobactins for growth and virulence of M. tuberculosis is supported by substantial in vitro and in vivo evidence. 5 Therefore inhibition of mycobactin biosynthesis 6 or antagonism of mycobactin function 7 represents an attractive strategy for the development of a new class of antitubercular agents.The biosynthesis of the mycobactins is initiated by MbtA, an adenylate forming enzyme, which activates salicylic acid 5 at the expense of ATP to form salicyladenylate 6 that remains tightly aldri015@umn.edu. Supporting Information Available: Experimental procedures, compound characterization data and 1 H and 13 C NMR of compounds reported herein, details of the [ 32 P]PPi-ATP exchange assay to determine K app I values, molecular modeling, and growth inhibition assay of M. tuberculosis H37Rv under iron-deficient conditions.

Siderophore-Based Iron Acquisition and Pathogen Control

“…Related aminoacyl sulfamoyl adenosines were shown in previous studies to act as potent inhibitors of NRPS and non-NRPS A domains (94,210). The in vitro and in-culture inhibition efficacy of SAL-AMS was confirmed in further studies (215,303,304,324). Due to the in vitro IC 50 values, which were in the range of the enzyme concentrations used, and the observed noncompetitive inhibition of the analogue with respect to salicylate, SAL-AMS was suggested to be a tight binding inhibitor (91 zyme inhibition were made during further studies with the same compound and several derivatives thereof; however, the compounds were always found to be fully competitive for both ATP and the corresponding aryl acid (44,215,304).…”

“…Further studies aimed to improve the overall stability and the anticipated ADMET (i.e., absorption, distribution, metabolism, elimination, and toxicology) profile (228a) of the SAL-AMS parent compound. The initially preferred sulfamate linker was identified as being potentially unstable due to the expulsion of the 5Ј-O-sulfamoyl moiety through spontaneous hydrolysis or cyclonucleoside formation (303,324). The introduction of an acylsulfamide function led to an analogue with the highest in-culture activity against M. tuberculosis that has been reported so far for an aryl acid A domain inhibitor (303) (Fig.…”

“…9). The replacement of the sulfamoyl group by a ␤-ketosulfonamide linkage, which was intended to prevent hydrolysis leading to the possible generation of cytotoxic sulfamoyladenosines, had an impaired effect on activity both in vitro and in vivo (324). Subsequent studies of docking to the MbtA active site (based on the DhbE X-ray structure) revealed a preference for analogues that are able to adopt a planar geometry of aryl acid and linking group as observed for the native acyl phosphate in the DhbE structure.…”

Characterization of Peptide Chain Length and Constituency Requirements for YejABEF-Mediated Uptake of Microcin C Analogues

“…A crucial portion of such an inhibitor scaffold is the linker between the amino acid and the adenosine moiety, which needs to be metabolically stable (13). Many different linkers have been developed as surrogates for the natural labile acylphosphate linkage (2,15,18). Aminoacyl-sulfamoyl adenosines were found to be the most potent analogues and proved to be nanomolar inhibitors of their corresponding aaRSs (3,12,16).…”

Multisubstrate adduct inhibitors: Drug design and biological tools

“…Using this finding, Aldrich et al developed new bisubstrate analog inhibitors of salicyl-AMP, with an acylsulfamate linkage mimicking the acyl-adenylate intermediate (Scheme 4) [19][20][21][22][23][24][25] . Biochemical analysis of MbtA using bisubstrate inhibitor has provided details of the reaction mechanism.…”