The thesis is divided into two parts. The first part describes the studies on the chemical constituents of Alstonia macrophylla and alstonia scholaris. The second part deals with the natural products of marine origin namely marine alga, Laurencia pinnatifida and marine animals zoanthid (an unidentified species) and aplysia Juliana.
Investigation of the alkaloidal contents of alstonia macrophylla led to the isolation of two new alkaloids along with two others which had been previously reported from other sources 1. Alstonmide (33) J.Nat. Prod., accepted fro publication. 2. Demethoxyalstonamide (40) Prod., accepted fro publication. 3. Vincorine (41) Planta medica submitted for publication 4. 3,4,5, -Trimethoxybenzoylvincamajine (42) Planta medica submitted for publication
The leaves of Alstonia scholaris were investigated which led to the isolation of a new alkaloid along with a previously reported one: 5. 10,20 –Z-vallesamine (43) Heterfocycles, 26 (2) 413 (1987) 6. 19,20-E-Vallesamine (48) Heterocycles, 26 (2) 413 (1987)
The second part of the thesis comprises studies on the chemistry of flora and fauna of the Arabian sea. Chemical investigation of Laurencia pinnatifida, Aplysia Juliana and an unidentified species of Zoanthid led to the isolation and structure elucidation of the following compounds. 1. Pinnatacane (49) Phytochemistry 27 (12), 3879 (1988) 2. Rearranged chamigrene acetate (56) Phytochemistry, submitted for Publication. 3. Pinnatifene (57) Phytochemistry, submitted for Publication. 4.Angasiol acetate (62) Phytochemistry, Accepted for Publication
Investigation on the sea hare Aplysia Juliana led to the isolation of angasiol acetate. The same compound has been isolated by us from Laurencia pinnatifida: Angasiol acetate (62) J. Nat. Prod. Submitted for Publication.
An unidentified species of the marine animal Zoanthid was investigated which led to the isolation of a new alkaloid along with two previously reported from other sources. These belong to a new class of alkaloids: 1. Zoanthaminone (67) Tetrahedron lett., 30 (49) 6825 (1989) 2. Zoanthamine (68) Teterahedron lett., 30 (49( 6825 (1989) 3. Zoanthamide (69) Tetrahedron lett., 30 (49) 6825 (1989)..
Modern spectroscopic techniques, including two dimensional NMR experiments, (COSY-45, 2D J-resolved, NOESY, hetero-COSY, COLOC) were employed to elucidate the structure of the above mentioned compounds. BB and DEPT experiments were carried out to determine the multiplicities of the carbon atoms. The stereochemistry at various asymmetric centres was established by noe measurements. The absolute configuration of some compounds was determined through X-ray crystallographic techniques.