The Crystal and Molecular Structure of Albocycline

Abstract

Abstract The detailed molecular geometry of albocycline (C18H28O4) has been examined by X-ray crystal analysis. The crystals are monoclinic, with four molecules in a unit cell with dimensions of a=16.177(2), b=9.562(1), c=11.742(2) Å, and β=90.43(1)°; the space group is P21. 3062 unique intensity data were collected on a four-circle diffractometer with graphite-monochromated Mo Kα radiation. The structure was elucidated by the Monte Carlo direct method, using the 30 reflections with the greatest |E| values as the starting set; the 174th random phase set led to the correct solution. The R value reached 0.057 by block-diagonal least-squares refinements. The two crystallographically-independent molecules are connected by two O–H···O hydrogen bonds, forming a hydrogen-bonded dimer. The conformations of the fourteen-membered macrolide rings in these two molecules are considerably different from each other; e.g., great differences of 165, 153, and 108° are found for the torsion angles around the C(4)–C(5), C(6)–C(7), and C(7)–C(8) single bonds respectively.