SYNTHESES, STRUCTURES, AND ENZYMATIC EVALUATIONS OF HEMIACYLCARNITINIUMS, A NEW CLASS OF CARNITINE ACYLTRANSFERASE INHIBITORS

The syntheses of (2S,6R)-6-(carboxymethyl)-2-hydroxy-2,4,4-trimethylmorpholinium chloride (hemiacetylcarnitinium, HAC), (2S,6R)-6-(carboxymethyl)-2-ethyl-2-hydroxy-4,4-dimethylmorpholinium bromide (hemipropanoylcarnitinium, HPrC), and (2S,6R)-6-(carboxymethyl)-2-hydroxy-4,4-dimethyl-2-phenylmorpholinium chloride monohydrate (hemibenzoylcarnitinium, HBC) are described. The crystal structure of HAC is reported and compared with crystal structures of HPrC, HBC, carnitine.HCl, acetylcarnitine.HCl, and acetylcarnitine.HCl.H2O. HAC, HPrC, and HBC inhibit carnitine acetyltransferase (CAT) activity from multiple biological sources. The best inhibitor, HAC, has K(i) of 69 +/- 5-mu-M with rat liver peroxisomal CAT. HAC binds more strongly than the natural substrate (and isomer), acetylcarnitine. HAC also strongly inhibits, K(i) = 92 +/- 14-mu-M, CAT from rat heart mitochondria. HPrC inhibits pigeon breast CAT with a K(i) of 200 +/- 30-mu-M. HBC inhibits pigeon breast CAT, rat heart mitochondrial CAT, rat liver mitochondrial CAT, and rat liver peroxisomal carnitine octanoyltransferase (COT), with values of K(i) of 3500 +/- 500, 2400 +/- 70,1670 +/- 70, and 1100 +/- 100-mu-M, respectively. Racemic 6-(carboxymethyl)-2-hydroxy-2-pentadecyl-4,4-dimethylmorpholinium bromide (hemipalmitoylcarnitinium, HPC) strongly inhibits (K(i) = 2 +/- 0.3-mu-M) beef liver mitochondrial CPT(i). In summary, hemiacylcarnitiniums show promise as a general class of carnitine acyltransferase inhibitors.