(1) is a polyol macrolide with a molecular weight of 2859 mu. As one of the degradation reactions, cross-metathesis of 2, which is a methyl ester of 1, with ethylene was performed to give the C33–C42 degradedfragment 4. The absolute configuration of 4 was estimated to be (36S,40S) by Mosher method. Stereoselectivesynthesis of 4 was achieved in 14 steps from l-aspartic acid. Synthetic bis-(S)- and