Intramolecular cyclization of erythromycin A (I) under acidic conditions yields its 8,9-anhydro-6,9-hemiketal derivative (II). Subsequent intramolecular trans-lactonization of (II) under basic conditions produces the ring-contracted compound, LY267108. It has also been synthesized from erythromycin in a single step by heating the latter in a 3:1 mixture of pyridine and acetic acid.