Studies on Macrocyclic Lactone Antibiotics. III. Skeletal Structure of Azalomycin F4a

The skeletal structure of azalomycin F4a (1) was determined on the basis of available data about the physicochemical properties of F4a and about the structures of the degradation products of this compound and of its derivatives. The structure was found to consist of a 36-membered lactone ring bearing multiple hydroxy functions, a diene and a dienoic ester group, as well as a side chain with an N-methylguanidine moiety as its terminal. One of the hydroxyl groups on the lactone ring forms a hemiketal ring with the keto group on a ring carbon, and another hydroxyl group forms a hemiester with a malonic acid moiety.