A method for preparing a fumarate salt of a compound represented by Formula (II):
##STR1##
(wherein R1 represents a hydrogen atom or a lower alkyl group,
and R2 represents a lower alkyl group), which comprises carbamating
a compound represented by Formula (I):
##STR2##
(wherein R1 represents a hydrogen atom or a lower alkyl group),
removing all carbamate groups from this compound, alkylating the nitrogen atom
at the 3-position of the desosamine ring in the resulting compound to give
the compound represented by Formula (II), and converting this compound into a fumarate
salt, wherein the compound represented by Formula (I) is carbamated in the presence
of a cyclic ether or a carboxylic ester. This method enables efficient preparation
of high-quality erythromycin derivatives.
