Crystal and Molecular Structure of 9-deoxo-9a-ethyl-9a-aza-9a-homoerythronolide A

The title compound is the 15-membered aglycone ring of the N-ethyl derivative of the new semisynthetic macrolide antibiotic 9-deoxo-9a-aza-9a- homoerythromycin A. Its molecular and crystal structure has been determined from the diffractometer X-ray intesity data and refined by the least-squares method to the reliability index R= 0.064. The crystals are orthorhombic, space group P2i2i2i, with cell parameters a = 17.784 (5), b = 22.009 (5), c = 13.675 (3) A. Although the molecular structure is similar to the analogous N-methyl derivative, as well as to other compounds with such 15-membered aglycone rings, the packing of molecules in the crystal structure is significantly different In the present structure, all hydroxyl-hydrogen atoms of the aglycones take part in the hydrogen bondings between neighbouring molecules forming helices around each screw diad axis. The helices are interconnected by an additional hydrogen bond