X-RAY STRUCTURAL STUDIES OF SOME NATURAL PRODUCTS FROM RAUWENHOFFIA SIAMENSIS SCHEFF., PRISMATOMERIS MALAYANA RIDL., CRATOXYLUM FORMOSUM SSP. PRUNIFOLUM AND ANDROGRAPHIS PANICULATA NEES PLANTS
| Presenter | : | NG SHEA LIN |
| : | - | |
| Date | : | 30 / 8 / 2007 |
| Time | : | 10.00 AM |
| Venue | : | BILIK PERSIDANGAN SEMENTARA (CEMACS),ARAS 1, PUSAT PENGAJIAN SAINS FIZIK |
| Sypnosis | : | In this thesis five new structures in the natural product compounds have been solved by single crystal X-ray crystallography method. The structure 1-(2,4-dihydroxy-6-methoxyphenyl)-3-(4-methoxyphenyl)propan-1-one, C17H18O5, which was isolated from the leaves of Rauwenhoffia siamensis Scheff has two crystallographically independent molecules in the asymmetric unit. The dihedral angle between the two benzene rings is 80.81 (7)o in one molecule and 65.89 (7) o in the other. The symmetry related molecules are linked via O—H---O intermolecular hydrogen bonds to form chains along [201] direction. This structure crystallized in the monoclinic system with the space group P21/c. The structure of 1-3-dihydroxy-2-methyl-9,10-anthraquinone, C15H10O4, which was isolated from the roots of Prismatomeris malayana Ridl., are coplanar. Intramolecular O—H---O and C—H---O hydrogen bonds can be observed in the molecular structure. The molecules form centrosymmetric hydrogen-bonded dimers via intermolecular O—H---O hydrogen bonds. The crystal structure is further stabilized by weak π–π interactions. This structure crystallized in the monoclinic system with the space group P21/c. For the structure of 12-(1,1-dimethyl-2-propenyl)-5,9,10-trihydroxy-2,2-dimethyl-2H,6H-pyrano[3,2-b]xanthen-6-one, C23H22O6, the xanthene ring system is essentially planar and the chromene ring is in a screw-boat conformation. The 1,1-dimethyl-2-propenyl substituent is coplanar with the attached ring. O—H---O intramolecular hydrogen bonds are observed in the structure. The molecules form centrosymmetric hydrogen-bonded dimers via weak intermolecular C—H---O interactions. The molecules are linked by intermolecular O—H---O hydrogen bonds to form a one-dimensional chain along [010] direction. This structure crystallized in the monoclinic system with space group P21/c. The structure of 3,19-(2-bromobenzylidene)andrographolide, C27H33BrO5, an andrographolide derivative, was semi-synthesized using andrographolide as a starting material. The structure contains three fused six-membered rings adopting chair conformations and a five-membered ring adopting an envelope conformation. The 2-bromophenyl group is twisted away from the attached ring. O—H---O hydrogen bonds in the structure form chains along the b axis which are interlinked via C—H---O interactions. This structure crystallized in the orthorhombic system with space group P212121. |
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