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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 P212121, 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.

crystal structure, 15-membered macrolide antibiotic, azalide

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