[Highlights from 43 years of chemistry of naturally occurring nitrogen-containing heterocycles. (1). Syntheses and structure determinations of benzo[a]quinolizidine-type and indolo[2,3-a]quinolizidine-type alkaloids isolated from several plants].

Nineteen benzo[a]quinolizidine alkaloids (1-19) isolated so far from Alangium plants can be classified into four types (I-IV) according to their chemical structures. Studies on racemic and chiral syntheses of these I-IV-type alkaloids are reviewed with particular emphasis on the strategies and tactics for the syntheses employed by the author. It has been found that racemic syntheses of all of these types of alkaloids are possible through the "lactim ether route" or the "3-acetylpyridine route"; and chiral syntheses, through the "cincholoipon-incorporating route" or the "chiral lactim ether route". As a result of such total syntheses, the structures and absolute configurations of four II-type, two III-type, and two IV-type Alangium alkaloids have been established. Extensions of the "chiral lactim ether route" to the syntheses of the Ochrosia alkaloid (-)-ochropposinine [(-)-93g], the Neisosperma alkaloid (-)-ochromianine [(-)-97], and the Ophiorrhiza alkaloid (-)-ophiorrhizine [(-)-98] have unequivocally established the absolute stereochemistries of these three indolo[2,3-a]-quinolizidine alkaloids.