Oximes natural occurrence

Two minor alkaloids were also isolated from B. zeylanica timber. The structure of one of these, C1oN8N202, mp 223-224°C, was revised from 3,4-dihydroxy-2,2 -bipyridine (18) to 8-hydroxyquinoline-4-carbaldehyde oxime (2) based on synthetic, NMR and nuclear overhauser effect (NOE) difference NMR spectroscopic evidence (19). Natural occurrence of oximes, although rare in higher plants, is not without precedence, and the essential oil of Ruta montana L. has been reported to contain the bis-oxime of 3,4-hexanedione (20). The structure of the nonpolar minor alkaloid broussonetine, C22H16N2O4, mp 238-239°C, was elucidated as 3,4-bis(8-hydroxyquinolin-4-yl)-y-butyrolactone (4) (21). 

Flavanones.—Most of the recent literature on flavanones concerns their natural occurrence, but the oxidation of 4-oximinoflavan with SeOi in aqueous dioxan has provided a means of reclaiming flavanone from its oxime some flavone and a little 3,3 -biflavonyl were also produced.A method has been described for separating flavanones and flavones, using commercial high-performance t.l.c. plates. The Rf values of the components varied considerably, according to the proportion of water in the eluting liquid. An extensive study has been made of the behaviour of flavanones in the mass spectrometer. 

Amino-5-deoxy-D-mannopyranose (1), whose natural occurrence Is reported In Section 1, and l,5-dldeoxy-l,5-lmlno-D-mannltol (39) have been prepared as shown In Scheme and their ability to Inhibit o- and 3-D-mannosldases studied. Reduction of the oxime (Mo) led to a separable mixture of D-manno-gtmlne (Ml) and Its L-gulo-Isomer, compound (Ml) being either hydrolyzed In the presence... 

The abundance of diverse oximes as naturally occurring products is attributed, in general, to complicated metabolic processes that include enzyme-induced oxidation of either amino acids or biogenic amines, as well as to the relatively low reactivity of oximes compared to HA. The co-occurrence of HA and a variety of carbonyl-containing molecules in plants and animals may also contribute to the formation of the oxime bond in nature. 

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