One positioning system of method and apparatus for weak data-frame sync IN.

摘要

The present invention provides a method for preparing an ester of betulin-3-acetate including alcoholyzing betulin 3,28-dibenzoate; a method for preparing betulin-3-acetate including: (1) acylating betulin to provide betulin 3,28-dibenzoate and (2) alcoholyzing betulin 3,28-dibenzoate to provide betulin-3-acetate; and a process for preparing betulinic acid including: (1) acylating betulin to provide betulin 3,28-dibenzoate; (2) alcoholyzsis betulin 3,28-dibenzoate to provide betulin-3-acetate; (3) oxidizing betulin-3-acetate to provide betulinic aldehyde-3-acetate; (4) oxidizing betulinic aldehyde-3-acetate to provide betulinic acid-3-acetate; and (5) deprotecting betulinic acid-3-acetate to provide betulinic acid.