Abstract The last step of Budesonide synthesis is acetalization of 16��-hydroxyprednisolone with n-butyraldehyde while a chiral 22-C is newly formed.Currently the marketed product is approximately a 1��1(molar ratio) mixture of the two diastereoisomers, 22R and 22S.Since later studies demonstrated therapeutic superiority of R over S, studies were launched here with an aim to raise the ratio of R in the product.Results showed that at 25 �� with perchloric acid as catalyst in dichloromethane for 3 h, a 96% yield of a product containing 22R to 22S as 85��15(molar ratio) was obtained.
2005, Vol. 22 
