Studies on nitrogen containing secondary metabolites from terrestrial and marine origin

Graduation date: 2002PART I. A deuterium exchange analysis of 2,5-dihydroxyacetanilide (5)\ud in the absence and presence of DHAE II was performed to test the\ud nucleophilicity of the substrate in the absence and presence of catalyst. In\ud addition, inhibition studies using 1,4-dihydroxybenzene were performed to\ud determine the role that the N-acetyl side chain group plays in the formation of a stable substrate-enzyme complex. 1,4-Dihydroxybenzene was found to be a\ud weak inhibitor, indicating that the N-acetyl functionality may play a crucial role in forming stable enzyme-substrate interactions. The synthesis of\ud dihydroquinoline 7 was pursued to investigate the enzyme substrate interactions\ud between DHAE and a substrate where the N-acetyl side chain has been fixed to a\ud particular orientation. Efforts towards formation of the C6-C7 bond as a key\ud step in the synthesis of dihydroquinoline 7 using palladium couplings,\ud organocuprates, Lewis acid catalysts, and aza-Claisen reactions were pursued.\ud To complement the results obtained, the electron distribution in amide 21 was\ud calculated using Semi Empirical methods. The results revealed that the electron\ud density in the aromatic ring is centered around C4, suggesting that this is the\ud most nucleophilic carbon in the ring.\ud PART II. Slagenins A (1), B (2), and C (3) were synthesized by β-functionalization\ud of olefin 14. The desired tetrahydrofuroimidazolidin-2-one system was achieved by intramolecular oxidative addition of alcohol 4 to the\ud imidazolone ring. When this reaction was carried out in the presence of\ud methanol slagenins B (2) and C (3) were obtained in good yield. Heating 2 and\ud 3 in aqueous acid gave slagenin A (1) as the sole product. (Z)-debromoaxinohydantoin (17) was synthesized by intramolecular cyclization of\ud α-methoxy imidazolone 11b under acidic conditions followed by a double\ud oxidation reaction to furnish the hydantoin-lactam functionality. These\ud conditions were originally developed for a practical synthesis of the related\ud alkaloid (Z)-debromohymenialdisine (20). A series of acid and base catalyzed\ud reactions of imidazoles bearing an α-β unsaturated system or a β-halogen\ud functionality showed that cyclizations via an S[subscript N]2 path favor formation of an\ud oxazoline ring system. Preliminary studies using pyrrolocarboxamideacetals\ud suggest that β-ketone 73 would be an appropriate substrate for the formation of\ud the pyrrolopyrazine system in the agelastatins