Diastereoselective concise syntheses of the polyhydroxylated alkaloids DMDP and DAB
摘要:
A diastereoselective concise synthesis of the iminosugars DMDP and DAB is presented starting from L-xylose and affording the two alkaloids in good yields of 35% and 22% over seven and eight steps, respectively. The Petasis borono-Mannich reaction of 3,5-di-O-benzyl-L-xylofuranose with benzylamine and (E)-styrylboronic acid served as the nitrogen-introducing key step furnishing the new C-N bond in an entirely diastereoselective manner. A chemo- and regioselective O-mesylation followed by an intramolecular S(N)2-cyclisation allowed the formation of the pyrrolidine ring. Ozonolysis of the styryl double bond and subsequent reduction to form the C-5 hydroxymethyl substituent followed by hydrogenolysis of the benzyl protecting groups concluded the DMDP synthesis. Furthermore, an unexpected fragmentation process during the ozonolysis reaction also gave access to the C-5 decarbinolated DMDP derivative DAB. (C) 2013 Elsevier Ltd. All rights reserved.
Synthesis of naturally occurring iminosugars from d-fructose by the use of a zinc-mediated fragmentation reaction
作者:Anne Lauritsen、Robert Madsen
DOI:10.1039/b605818c
日期:——
A short synthesis of 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) and a formal synthesis of australine are described. In both cases, D-fructose is employed as the starting material and converted into a protected methyl 6-deoxy-6-iodo-furanoside. Zinc-mediated fragmentation produces an unsaturated ketone which serves as a key building block for both syntheses. Ozonolysis, reductive amination with benzylamine