EVALUATION OF THE INHIBITORY ACTIVITY OF VARIOUS UNREPORTED CMP-NEU5AC DONOR CONGENERS ON GM3 SYNTHASE

A class of sialosides (down reported 3a-e, 4a-c, 5a-c and 5e), designed to inhibit the biological transfer of sialic acid 1 to the terminal portion of glycoconjugates, mediated by the enzymes sialyltransferases, was synthesized and their inhibitory activities was tested on a α-2,3 sialyltransferase, from Pasteurella multocida, and on GM3 synthase, present both as a cellular homogenate and in a cell line of HEK293 (Human Embryonic Kidney). The synthesized compounds 3a-e are congeners of the natural sialyl donor CMP-Neu5Ac 2 and incorporate some structural properties of the compound 3a, the only known inhibitor of GM3 synthase enzyme reported in a short note.1 Moreover, we synthesized also the lactones 4a-c and the peracetylated derivatives 5a-c and 5e in order to improve the cell permeability of their parent hydroxyl acids. The GM3 synthase activity was evaluated detecting the formation of the labeled GM3 in process using lactosyl-ceramide labelled ([3-3H(sphingosine)]LacCer] as acceptor, or labeled sphingosine ([3-3H] SPH) as unsialylated ganglioside precursor.3 Last procedure allowed to evaluate also the complete pattern of gangliosides formed in the cell in the presence or absence of inhibitors. All synthesized compounds were tested on GM3 synthase of HEK cellular homogenate. The more active acidic compounds were also tested on intact cell lines, improving their lipofilicity, by methyl esterification and after peracetylation. The free compounds 3b-c, 3e and 4c show an inhibitory activity always higher than 3a. Similarly the peracetylated methylester 5b-c and 5-e are more activity than 5a in intact cell lines. All compounds show an inhibitory activity higher on the cell homogenates than that on HEK cells. The lactones 4a-c were not active in cell lines probably since they do not cross the cell membrane as the peracetylated methyl ester 5a-e that are actives. The α-sialoside 5e resulted the most active. This is a very interesting result since evidences that the geometry at the anomeric centre of the glycosyl donor is not an exential requisite. However, all results together extend the knowledge on inhibitors of GM3 synthase and provide new structural information for the development of other novel STs inhibitors.