Considering that there were only two possible configurations for the oxygen bridge between C-7 and C-10,acomparison of time-dependent density functional theory (TDDFT) calculated optical rotations (OR) with experimental optical rotation was applied. The negative calculated OR value (0.98) for 5S,10S,7S, which was in agreement with the negative experimental OR value of 13.6, suggested that the oxygen bridge between C-7 and C-10 was b-oriented (The calculated OR for 5S,10R,7Rwas a positive value of þ0.86).