ABSTRACT
The crystal structures of rubescin D (1, C26H30O5) and monadelphin A (2, C30H36O11), bioactive molecules of the vilasinin and gedunin classes of limonoids, respectively, are reported for the first time and the synthons affecting their crystal packings are analyzed on the basis of their occurrences in molecules in the Cambridge Structural Database that share the same moieties. Rubescin D, 1, crystallizes in the space group P21 and its molecular structure consists of three six-membered rings A, C and D having, respectively, envelope, twist-boat and half-chair conformations, and three five-membered rings with half-chair (B and E) and planar conformations (F). Many synthons found in the crystal packing of 1 are in agreement with expectations derived from molecules displaying the same moieties. However, the secondary alcohol-ketone O-H...O=C synthon, which has a low occurrence (2.9%), contributes much to the layered packing, while the furan-ketone Csp2-H...O=C and secondary alcohol-epoxide O-H...OC2 synthons usually found in these compounds (occurrences of 20.6 and 17.6%, respectively) are missing. The packing of 1 is close to that of ceramicine B (3), but is completely different from that of TS3 (4), suggesting that the absence of the epoxide group in 3 would have favoured the furan-secondary alcohol Csp2-H...OH synthon and that the missing hydroxy group in 4, a strong hydrogen-bond donor, would have favoured the involvement of water molecules in the crystal packing. The molecular structure of monadelphin A, 2, consists of four six-membered fused rings (A, B, C and D) and one five-membered ring (E); they have twist-boat (A and C), chair (B), screw-boat (D) and planar (E) conformations. The molecule crystallizes in the space group P212121 with the contribution of many synthons usually found in compounds having the same moieties. However, the secondary alcohol-acetate O-H...OOC and secondary alcohol-ketone O-H...O=C synthons (occurrences of 16.7% each in these compounds) are missing. The furan-acetate Csp2-H...OOC synthon not observed in these compounds greatly contributes to the layered packing of 2. The layered packing is very close to those of 7-oxogedunin (5) and 6-dehydro-7-deacetoxy-7-oxogedunin (6), which both crystallize in the space group P21.
Subject(s)
Acetates/chemistry , Furans/chemistry , Ketones/chemistry , Crystallization , Crystallography, X-Ray , Hydrogen Bonding , Molecular ConformationABSTRACT
The title limonoid compound, C26H28O5·0.5H2O (TS3) [systematic name: (3aS,3bS,4aS,5aS,6S,7aR,8aR,8bS,11aR)-6-(furan-3-yl)-3a,5a,8b,11a-tetra-methyl-3a,4a,5,5a,6,7,7a,8b,11,11a-deca-hydro-oxireno[2',3':4b,5]oxireno[2'',3'':2',3']cyclo-penta-[1',2':7,8]phenanthro[10,1-bc]furan-3(3aH)-one hemihydrate], crystallizes with two independent mol-ecules (1 and 2) in the asymmetric unit and one water mol-ecule. TS3 is composed of three six-membered rings (A, C and D), three five-membered rings (B, E and F) and two epoxide rings. A group of five fused rings (A-E) is bonded to a furan ring (F) with a Csp3-Csp2 bond [1.500â (3)â Å in mol-ecule 1 and 1.499â (3)â Å in mol-ecule 2]. The absolute structures of the mol-ecules in the crystal were determined by resonant scattering; Flack parameter = 0.05â (5). In the crystal, the individual mol-ecules stack in columns along the b-axis direction. The water mol-ecule bridges mol-ecules 1 and 2 via Owater-Hâ¯O and C-Hâ¯Owater hydrogen bonds. Together with further C-Hâ¯O hydrogen bonds, linking mol-ecules 1 and 2, the columns are linked to form slabs parallel to the ab plane. Within each column, mol-ecules are also linked via C-Hâ¯π inter-actions involving the five-membered furan (F) rings.
ABSTRACT
Three new limonoids, rubescins A-C (1-3), and three known compounds including, havanensin type limonoid TS3 (4), ß-sitosterol, and stigmasterol were isolated from the root bark of Trichilia rubescens. Their structures were elucidated by means of extensive spectroscopic analyses, particularly one dimensional (1D)- and 2D-NMR techniques in conjunction with mass spectrometry. Rubescins A-C (1-3) and limonoid TS3 (4) were evaluated for their protective effects against oxidative stress induced in HC-04 cells by H2O2. Compound (1) showed strong inhibitory effects on lactase dehydrogenase (LDH) leakage, being as active (IC50 value of 0.0026 µM) as the positive control quercetin (IC50 value of 0.0030 µM).
