ABSOLUTE-CONFIGURATIONS OF 3 ENT-BEYERENE DERIVATIVES

(1): 11-beta,17-Bis(4-bromobenzoyloxy)-9-beta-hydroxy-ent-beyerene, C34H38Br2O5, M(r) = 686.5, orthorhombic, P2(1)2(1)2(1), a = 6.1686 (12), b = 14.613 (3), c = 32.935 (7) angstrom, V = 2969 (1) angstrom 3, Z = 4, D(x) = 1.536 g cm-3, lambda-(Mo K-alpha) = 0.71069 angstrom, mu = 27.43 cm-1, F(000) = 1408, T = 173 K, R = 0.0347 and wR = 0.0358 for 3064 reflections [I(o) greater-than-or-equal-to 3-sigma-(I(o))]. (2): 7-beta,17-Bis(4-bromobenzoyloxy)-9-beta-hydroxy-ent-beyerene, C34H38Br2O5, M(r) = 686.5, monoclinic, P2(1), a = 12.6424 (15), b = 6.8353 (12), c = 18.496 (2) angstrom, beta = 101.901 (9)-degrees, V = 1564.0 (4) angstrom3, Z = 2, D(x) = 1.458 g cm-3, lambda-(Mo K-alpha) = 0.71073 angstrom, mu = 26.03 cm-1, F(000) = 704, T = 173 angstrom, R = 0.0336 and wR = 0.0361 for 4610 reflections [I(o) greater-than-or-equal-to 3-sigma-(I(o))]. (3): 17-(4-Bromobenzoyloxy)-9-beta,11-beta-epoxy-7-beta-hydroxy-ent-beyerene, C27H33BrO4, M(r) = 501.5, orthorhombic, P2(1)2(1)2(1), a = 6.1315 (7), b = 18.389 (3), c = 21.109 (3) angstrom, V = 2380.0 (6) angstrom 3, Z = 4, D(x) = 1.399 g cm-3, lambda-(Mo K-alpha) = 0.71073 angstrom, mu = 17.38 cm-1, F(000) = 1048, T = 198 K, R = 0.0325 and wR = 0.0344 for 2292 reflections [I(o) greater-than-or-equal-to 3-sigma-(I(o))]. The absolute configurations of (1), (2) and (3) were determined by the eta (chirality/polarity) refinement which indicated that the molecular models refined belong to the correct configuration, namely, the ent-beyerene skeletal type. As a result, the biosynthetic pathways of (4) (9-beta,11-beta,17-trihydroxy-ent-beyerene), (5) (7-beta,9-beta,17-trihydroxy-ent-beyerene) and (6) (9-beta,11-beta-epoxy-7-beta,17-dihydroxy-ent-beyerene) are established as the ent-diterpenoid pathway. The three cyclohexane rings A, B and C are in chair conformations, whereas the five-membered rings are in envelope conformations. The hydroxyl group in each compound is involved in hydrogen bonding: (1) one intramolecular and one intermolecular bond; (2) one intramolecular bond; and (3) one intermolecular bond.