Thiodisaccharides with galactofuranose or arabinofuranose as terminal units: synthesis and inhibitory activity of an exo beta-D-galactofuranosidase.

Thiodisaccharides having beta-D-Galf or alpha-L-Araf units as non-reducing end have been synthesized by the SnCl(4)- or MoO(2)Cl(2)-promoted thioglycosylation of per-O-benzoyl-D-galactofuranose (1), its 1-O-acetyl analogue 4, or per-O-acetyl-alpha-L-arabinofuranose (16) with 6-thioglucose or 6-thiogalactose derivatives. After convenient removal of the protecting groups, the free thiodisaccharides having the basic structure beta-D-Galf(1-->6)-6-thio-alpha-D-Glcp-OMe (5) or beta-D-Galf(1-->6)-6-thio-alpha-D-Galp-OMe (15) were obtained. The respective alpha-L-Araf analogues 18 and 20 were prepared similarly from 16. Alternatively, beta-D-Galf(1-->4)-4-thio-3-deoxy-alpha-L-Xylp-OiPr was synthesized by Michael addition to a sugar enone of 1-thio-beta-d-Galf derivative, generated in situ from the glycosyl isothiourea derivative of 1. The free S-linked disaccharides were evaluated as inhibitors of the beta-galactofuranosidase from Penicillium fellutanum, being 15 and 20 the more active inhibitors against this enzyme.

Glycosphingolipids in Plasmodium falciparum. Presence of an active glucosylceramide synthase.

Malaria remains a major health problem especially in tropical and subtropical regions of the world, and therefore developing new antimalarial drugs constitutes an urgent challenge. Lipid metabolism has been attracting a lot of attention as an application for malarial chemotherapeutic purposes in recent years. However, little is known about glycosphingolipid biosynthesis in Plasmodium falciparum. In this report we describe for the first time the presence of an active glucosylceramide synthase in the intraerythrocytic stages of the parasite. Two different experiments, using UDP-[(14)C]glucose as donor with ceramides as acceptors, or UDP-glucose as donor and fluorescent ceramides as acceptors, were performed. In both cases, we found that the parasitic enzyme was able to glycosylate only dihydroceramide. The enzyme activity could be inhibited in vitro with low concentrations of d,l-threo-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP). In addition, de novo biosynthesis of glycosphingolipids was shown by metabolic incorporation of [(14)C]palmitic acid and [(14)C]glucose in the three intraerythrocytic stages of the parasite. The structure of the ceramide, monohexosylceramide, trihexosylceramide and tetrahexosylceramide fractions was analysed by UV-MALDI-TOF mass spectrometry. When PPMP was added to parasite cultures, a correlation between arrest of parasite growth and inhibition of glycosphingolipid biosynthesis was observed. The particular substrate specificity of the malarial glucosylceramide synthase must be added to the already known unique and amazing features of P. falciparum lipid metabolism; therefore this enzyme might represent a new attractive target for malarial chemotherapy.