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.
Synthesis of salacinol
Abstract Salacinol, a new type of α-glucosidase inhibitor discovered from the antidiabetic herb, was synthesized for the first time. Under the strategy that salacinol would be synthesized by the coupling reaction between 1,4-epithio- d -arabinitol and the cyclic sulfate of an erythritol derivative, the model coupling reactions between tetrahydrothiophene and versatile cyclic sulfate derivatives were undertaken. These experiments indicated that the 1,3-diol of the cyclic sulfate should be protected with the isopropylidene group, otherwise, even the benzylidene-protected cyclic sulfate decomposed during the reaction. Thus, the salacinol was synthesized using the cyclic sulfate of 1,3- O -isopypropylidene- d -erythritol. The resulting coupling product was deisopropylidenated to afford salacinol. A diastereomer of salacinol was also synthesized.
Cryostat use and tissue processing in Mohs micrographic surgery.
Information of cryostat use and reliability was collected from 130 members of the American College of Mohs Micrographic Surgery and Cutaneous Oncology. The Damon IEC International cryostat was utilized by 38% of the survey participants, followed by the Reichert Histostat (18%) and the LabTek/TissueTek (13%). Data were also collected on methods of frozen-section embedding and technical training.