Tetrazole and acylsulfonamide bioisosteric replacements of the carboxylic acid in a dual MCL-1/BCL-x(L) inhibitor are tolerated

Overexpression of the anti-apoptotic protein MCL-1 is associated with a plethora of human cancers, and it reduces the sensitivity of cancer cells to approved chemotherapies. Accordingly, the discovery of MCL-1 inhibitors is an active area of interest. Many inhibitors of the anti-apoptotic MCL-1 protein bear a crucial carboxylic acid that may engage Arg263 in the BH3-binding groove. We previously described the salicylic acid-based dual MCL-1/BCL-x(L) inhibitor 17cd, which is currently undergoing lead optimization. As part of that process, we wished to investigate bioisosteric replacement of 17cd's key carboxylic acid. Herein we describe the synthesis of a variety of analogues of a simpler analogue of 17cd presenting carboxylic acid surrogates. The acylsulfonamide and tetrazole motifs, which exhibit comparable pK(a)s to the carboxylic acid function, displayed similar, or better, binding affinities to MCL-1 and BCL-x(L) as the corresponding carboxylic acid-containing lead. Our best compound was acylsulfonamide 7d with a K(i) of 800 nM against MCL-1 and 1.82 mM against BCL-x(L), and demonstrated an improved effect on the viability of the HL60 acute myeloid leukemia cell line relative to the parent carboxylic acid-containing dual inhibitor from which it was derived.