Oxazoles of the Rutaceae

Oxazoles of the Rutaceae number some dozen alkaloids halfordinol (16) (6, 7), halfordine (17) (6, 8, 9), halfordinone (18) (6, 8), O-isopentenylhalfordinol 

The compounds and their sources are listed in chronological order of isolation in Table I. The majority of the Rutaceae oxazoles have been isolated from the Old World genera Halfordia, Aegle, Aeglopsis, and Micromelum Amyris is the 

Oxazoles of Rutaceae Reported Isolation and Structure Elucidation in Chronological Order 

Although the biosynthesis of 2-pyridyl-5-phenyloxazoles has not been studied, the likely veracity of this sequence has been borne out by the biosynthetic study of annuloline (1) (5) and the cooccurrence in the rutaceous genera Aegle and Amyris of oxazoles and open chain (3-phenylethylamides (11-13, 16, 18). In the biosynthesis of annuloline (1), the low incorporation of O-methylated precursors was a notable point (5) lending support to the possible intermediacy of quinone-methene type compounds such as 31 and 32 and the operation of either a cycliza-tion-alkylation (e.g., 32 to 33) process or a dehydrogenation-alkylation (e.g., 31 to 34) process. 

Aegle marmelos, which produces halfordinol (16) (7) and O-isopentenyl-halfordinol (19) (11), also accumulates the (3-phenylethylamides aegeline (35), A-2-methoxy-2-(4-methoxyphenyl)ethy lcinnamide (36), (V-2-ethoxy-2-(4-meth-oxyphenyl)ethylcinnamide (37), and A-2-methoxy-2-[(4-(3, 3 -dimethylallyl-oxy)phenyl]ethylcinnamide (38) (11). The coincidence in compounds 36, 37, 

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