Study On Synthesis Of Pyrrolizidine Alkaloids By Norrish â…¡ Cyclization Photochemical Reaction

Alkaloids are kinds of important nitrogenous alkaline natural organic compounds existing in organisms. Most of alkaloids have complicated ring systems, containing nitrogen atom as heterocycles. Pyrrolizidine alkaloids (PAs) are types of highly active alkaloids which widely exist in natural compounds. More than 600 species of PAs were isolated in natural products presently. The basic scaffold of pyrrolizidine alkaloids is consisted of a bicyclic moiety which arised from the coupling of tetrahydropyrrole and a hydroxyl-substituted tetrahydropyrrole via N-C coupling reactions. Most of the alkaloids contain ester substructure. Generally, the ammonia alcohol moiety is named necine, and the organic acid moiety is named necic acid.In this thesis, we designed a feasible synthetic route for Elibracteatinenice and Curassanecine from L-malic acid based on Norrish type II cyclization photochemistry. In order to synthesize precursor of photochemistry, compound (S)-methyl 4-(4-(tert-butyldimethylsilyloxy)-2-oxopyrrolidin-1-yl)-2-oxobutanoate, we synthesi- zed a series of compounds as 4-(2-bromoethyl)-2, 2-dimethyl-1,3-dioxolane, Methyl 3-hydroxy-4-(tosyloxy) butanoate, 4-(tert-butyldimethylsilyloxy) pyrrolidin-2-one, 2-(2, 2-dimethyl-1, 3-dioxolan-4-yl) ethanamine, 3-(tert-butyldimethylsilyloxy) pyrrolidine-2, 5-dione and (S)-5-(2-bromoethy l)-2, 2-dimethyl-1, 3-dioxolan-4-one from L-malic acid. Employing those six compounds to build up key intermediate (S)-4-(tert-butyldimethylsilyloxy)-1-(2-((S)-2,2-dimethyl-1,3-dioxolan-4-yl)ethyl)pyrrolidin-2-one, we will be able to abtain the precursor of photochemistry 2-13 via few more steps, then the bicyclic moiety will form under Norrishâ…¡cyclization photochemical reaction conditions, which providing the basic scaffold of pyrrolizidine alkaloids.