The thio-Mitsunobu reaction: a useful tool for the preparation of 2,5-anhydro-2-thio- and 3,5-anhydro-3-thiopentofuranosides.
The unprotected methyl L-arabinofuranosides, D-ribofuranosides and D-xylofuranosides are transformed into the corresponding S-acetyl-5-thio derivatives by the thio-Mitsunobu reaction. Mesylation and subsequent reaction with sodium hydrogen carbonate led, depending on the configuration of the intermediate, to 2,5-anhydro-2-thio- or 3,5-anhydro-3-thiopentofuranosides. Due to inversion at C-3 or C-2 during the intramolecular nucleophilic displacement the products exhibit L-lyxo-, D-arabino- or D-lyxo-configuration. Analogously, the methyl 2,3-anhydro-D-ribofuranosides yielded 5-thio-S-acetates with intact 2,3-oxirane groups, which were cyclised with sodium hydrogen carbonate by epoxide ring opening and concomitant ring closure to form exclusively 3,5-anhydro-3-thio-D-xylofuranosides. A related 3,5-anhydro-3-seleno-D-lyxofuranoside was obtained by reaction of a 3,5-di-O-mesyl-D-arabinofuranoside with sodium hydrogen selenide. Several X-ray diffraction analyses proved the structures of the products.
A Novel Synthesis of 2‘-Modified 2‘-Deoxy-4‘-thiocytidines from d-Glucose1
Novel 2‘-deoxycytidine antimetabolites, specifically several 2‘-modified 2‘-deoxy-4‘-thiocytidines, were synthesized as potential new antineoplastic agents. Methyl 3-O-benzylxylofuranoside was converted to a 1,4-anhydro-4-thioarabitol 24. Protection of the primary alcohol of 24 gave a common intermediate (15) which was useful for the synthesis of various 2‘-modified 2‘-deoxy-4‘-thionucleosides. Oxidation of the secondary hydroxyl group of 15, followed by the Wittig reaction or treatment with (diethylamido)sulfur trifluoride (DAST) produced 2-deoxy-2-methylene (26) and 2-deoxy-2,2-difluoro (34) derivatives, respectively. Unique Pummerer-type glycosylation between the corresponding sulfoxides and trimethylsilylated N4-acetylcytosine produced 2‘-deoxy-2‘-methylene- (10) and 2‘-deoxy-2‘,2‘-difluoro-4‘-thiocytidines (11). On the other hand, treatment of 15 with DAST introduced a fluorine atom with retention of the 2‘-stereochemistry, yielding 40. In contrast, the Mitsunobu reaction of 3-O-benzoyl derivative 53...
Complexities of Assessing the Disease Burden Attributable to Leishmaniasis
Among parasitic diseases, morbidity and mortality caused by leishmaniasis are surpassed only by malaria and lymphatic filariasis. However, estimation of the leishmaniasis disease burden is challenging, due to clinical and epidemiological diversity, marked geographic clustering, and lack of reliable data on incidence, duration, and impact of the various disease syndromes. Non-health effects such as impoverishment, disfigurement, and stigma add to the burden, and introduce further complexities. Leishmaniasis occurs globally, but has disproportionate impact in the Horn of Africa, South Asia and Brazil (for visceral leishmaniasis), and Latin America, Central Asia, and southwestern Asia (for cutaneous leishmaniasis). Disease characteristics and challenges for control are reviewed for each of these foci. We recommend review of reliable secondary data sources and collection of baseline active survey data to improve current disease burden estimates, plus the improvement or establishment of effective surveillance systems to monitor the impact of control efforts.