2′,4″-O-Bis(trimethylsilyl) 6-O-methylerythromycin A 9-O-(1-methoxycyclohexyl) oxime was regioselectively synthesized and characterized and its crystal structure was determined by the single crystal X-ray structure analysis. The crystal belonged to tetragonal system with I4 space group and a=b=2.9720(4) nm, c=1.4939(3) nm, V=13.195(4) nm3, Z=8, R=0.0587, wR=0.1263, S=1.004 for 11526 unique reflections. The crystal structure shows that the attack of methylation reagents was blocked by 9-oxime ether as result, a hydrogen bond formed between 11-OH and nitrogen of 9-oxime, and the attack of methylation reagents was blocked by 9-oxime ether, whereas the orientation of 6-OCH3 was located in the cave surrounded by several rings so that 6-OH was unique one to be exposed to methylation reagents. However, the congestion around 11-OH was loosened, which resulted from the orientation of protective group so that much 6,11-O-dimethyl product was yielded. Additionally, the crystal structure of 2′,4″-O-bis(trimethylsilyl) erythromycin A 9-O-(1-methoxy-1-methylethyl) oxime was first disclosed as a comparison.
