The Molecular and Crystal Structure of an Oxindole Alkaloid (6-Hydroxy-2′-(2-methylpropyl)-3,3′-spirotetrahydropyrrolidino-oxindole)

Abstract

A previously unknown alkaloid of molecular formula C15H20O2N2 was isolated from the dried root bark of EleagnusCommutata (Wolf willow or Silverberry). An X-ray analysis was undertaken to complete the structural characterization of the molecule. Columnar crystals obtained from diethyl ether have the unit cell constants, a = 13.1949(10) Å, b = 9.4525(6) Å, c = 12.1186(6) Å, β = 109°47(1)′ and belong to space group P21/c. The structure was solved using an automated symbolic addition procedure and refined by block-diagonal least-squares to weighted and unweighted R factors of 6.25% and 4.30%, respectively. The previous structural studies were shown to be essentially correct except for the incorrect placement of the phenolic hydroxyl on C(5) of the oxindole nucleus. The correct molecular structure is implied by the systematic name given. The —OH group engages in two intermolecular hydrogen bonds with the two nitrogen atoms, but the carbonyl moiety is not involved in any such interactions.