Rational Design, Synthesis, and Preliminary Structure–Activity Relationships of α-Substituted-2-Phenylcyclopropane Carboxylic Acids as Inhibitors of Salmonella typhimurium O-Acetylserine Sulfhydrylase

Abstract

Cysteine is a building block for several biomolecules that are crucial for living organisms. The last step of cysteine biosynthesis is catalyzed by O-acetylserine sulfydrylase (OASS), a highly conserved pyridoxal 5'-phosphate (PLP)-dependent enzyme, present in different isoforms in bacteria, plants, and nematodes, but absent in mammals. Beside the biosynthesis of cysteine, OASS exerts a series of "moonlighting" activities in bacteria, such as transcriptional regulation, contact-dependent growth inhibition, swarming motility, and induction of antibiotic resistance. Therefore, the discovery of molecules capable of inhibiting OASS would be a valuable tool to unravel how this protein affects the physiology of unicellular organisms. As a continuation of our efforts toward the synthesis of OASS inhibitors, in this work we have used a combination of computational and spectroscopic approaches to rationally design, synthesize, and test a series of substituted 2-phenylcyclopropane carboxylic acids that bind to the two S. typhymurium OASS isoforms at nanomolar concentrations.

Cyclopropane-1,2-dicarboxylic acids as new tools for the biophysical investigation ofO-acetylserine sulfhydrylases by fluorimetric methods and saturation transfer difference (STD) NMR

“…On a similar vein, when the ester moiety and the acid are in trans stereo-relationship, the affinity is higher than that measured on the cis stereoisomer. In a more comprehensive picture (Figure 2), this small set of molecules has corroborated the findings partially stemmed also from our previous studies 25,27 : assuming the cyclopropanecarboxylic acid as the pharmacophore, substituents at C-2 showing a hydrophilic character must be kept in a cis stereo-relationship with the C-1 carboxylic group, whereas less hydrophilic substituents must maintain a trans stereo-relationship.…”

“…Since for the most active compounds the main structural motif (the 2-phenylcyclopropylcarboxylic moiety) is maintained, it can be reasonably assumed that the binding mode of these derivatives is similar to that already reported in our previous works [25][26][27] . To ascertain this hypothesis, and to correlate the data obtained from the STD-NMR experiments and the biochemical evaluation, a computational analysis of the binding mode of compound 23 with StOASS-A was performed.…”

“…Reacting benzyl cyanide and epichlorohydrin in the presence of sodium amide, at 90 C in benzene, the corresponding cyclopropyl alcohol was obtained, that on turn underwent basic hydrolysis to give the title compound 28 in 44% overall yields (Scheme 3). Attempts to synthesize the ethyl ester of 28 according to other reported procedures 27,30 failed to give the desired compound.…”

“…We have recently developed a series of substituted 2-phenylcyclopropane carboxylic acids that bound with high affinity to both the isoforms of Salmonella enterica serovar typhimurium OASS (StOASS) 27 . The main chemical feature was represented by the presence of a carboxylic acid moiety linked through a cyclopropane spacer, to a hydrophobic side chain in a trans configuration.…”

“…The rational design of the first inhibitors was based on the structure of SAT, that physiologically inhibits OASS activity upon formation of the cysteine synthase bioenzyme complex 22,23 ; in particular, it was considered that the carboxylic moiety of Ile267 of SAT is essential for the interaction between the two proteins [22][23][24] . Therefore, combining a structure-based with a ligand-based drug design approach, we planned and synthesized a series of cyclopropanecarboxylic acid derivatives that bind to both OASS isoforms at nanomolar concentrations [25][26][27] . In order to further refine the structure-activity relationships (SAR) around this class of derivatives, we herein report the design and synthesis of a series of cyclopropane-1,2-dicarboxylic acids variously functionalized.…”