A key element for rapid access to substituted methylketone derivatives was the generation of the fully elaborated CMK 12 (Scheme 2). The utility of the CMK moiety to prepare acyloxy- and hydroxy-substituted methylketones is well established. Elaboration of 10 in a sequence of deprotection/1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU)-mediated peptide couplings provided CMK derivative 12 in moderate yield with no epimerization observed. Reaction of 12 with various carboxylic acids in the presence of cesium fluoride at 60 °C provided acyloxymethylketones 13–28. Using this synthetic approach with substitution of P2 and amine capping structural elements provided inhibitors 3 and 29–31.