26 B CH2O 27 CH2-C-H CH C-O26 20 25S,25L,25βFneo 26 CH, a H=C-CH3 CH, CH O-C-026 CH H 25R,25D,25F,iSo 21 20O O HO CH2 O C CH2 CH2 C CH3 C H O O CH3 H 26 26 16 25 20 21 27 b b CH2 O C CH2 CH2 C CH3 C H O O H CH3 26 26 16 25 20 21 O 27 O HO a 25S,25L,25bF,neo 25R,25D,25aF,iso