Single crystal X-ray structures of the two 4-heptadecyl derivatives of (1R,5S)-3,6,8-trioxabicyclooctane

Article abstract of DOI:10.1016/0009-3084(95)02458-U

The single crystal structures of the two diastereomeric 4-heptadecyl derivatives of (1R,5S)-3,6,8-trioxabicyclo<3.2.1>octane have been determined by X-ray diffraction to be (1R,4R,5S)-heptadecyl-3,6,8-trioxabicyclo<3.2.1>octane (I) and (1R,4S,5S)-4-heptadecylo<3,6,8-trioxabicyclo<3.2.1>octane (II), respectively, which have an exo or axial 4-heptadecyl group, and an endo or equatorial 4-heptadecyl group, respectively.The structures of I and II had been suggested by their phase-sensitive 2D NOESY 1H-NMR spectra, but are now established unambiguously.These optically pure non-ionic lipid-like amphipathic molecules (I and II) represent the first 3,6,8-trioxabicyclo<3.2.1>octanes for which single crystal structures have been solved.Crystals of both isomer I and isomer II were orthorhombic with space group P2₁2₁2₁ and had unit cell dimensions of a = 9.586, b = 43.14, c = 5.289 Angstroem, and a = 7.34, b = 51.8, c = 5.636 Angstroem, respectively.The structures of I and II were both solved by using direct methods to R = 0.045 and R = 0.086, respectively.Both I and II pack in stacked bilayers with interdigitating and tilting hydrocarbon chains.The molecular and hydrocarbon cross sections are I: S = 50.70 Angstroem², Σ = 19.00 Angstroem² ; and II: S = 41.37 Angstroem², Σ = 18.26 Angstroem².Keywords: (1R,4R,5S)-4-heptadecyl-3,6,8-trioxabicyclo<3.2.1>octane; (1R,4S,5S)-4-heptadecyl-3,6,8-trioxabicyclo<3.2.1>octane; X-ray; Crystal structure; Molecular packing; Nonionic amphiphile