Synthesis of 7-Deoxypancratistatin from Carbohydrates by the Use of Olefin Metathesis

摘要

The stereocontrolled synthesis of (+)-7-deoxypancratistatin is described.The convergent synthesis has been achieved by two different strategies,both of which commence from a pentose and piperonal.The latter is converted into allylic bromide 7,which is then coupled with a protected methyl 5-deoxy-5-iodo-D-ribofurano-side in the presence of zinc metal.The first strategy involves a total of only 13 steps from D-ribose and piperonal,but suffers from a low yield in the zinc-mediated reaction between ribofurano-side 9,benzylamine,and bromide 7.The second strategy involves a total of 18 steps from D-xylose and piperonal.The former is converted into ribofura-noside 28,which is coupled with bromide 7 in the presence of zinc,and this is followed by ring-closing olefin metathesis.Subsequent Overman rearrangement,dihydroxylation,and deprotec-tion then affords the natural product.