Structural studies of some serrulatane diterpenes

Abstract

The crystal structures of methyl (15S)-7,8,16-trihydroxyserrulatan-19-oate (1) and 2,7,8,20-tetrahydroxyserrulat-14-ene (2) have been established by single crystal X-ray diffraction techniques at 295 K, being refined by least squares to residuals of 0.046 and 0.053 for 1 153 and 1 513 ‘observed’ reflections respectively. Crystals of (1) are orthorhombic, P2₁2₁2₁, a= 21.78(2), b= 18.42(2), c= 5.101(3)Å, Z= 4 while those of (2) are monoclinic, C2, a= 14.96(1), b= 12.315(6), c= 21.75(1)Å, β= 107.21(5)°, Z= 8. As well as establishing total relative stereochemistry in (1), an interesting intramolecular hydrogen-bonding system is observed, together with an alicyclic ring conformation differing from that found in the previously studied dihydroxyserrulatic acid (3). In (2), the two independent molecules of the asymmetric unit have different conformations, corresponding broadly to those of (1) and (3).