Lemon oil contains furocoumarin derivatives and is known to cause phototoxicity. In this study, lemon oil was fractionated, and its phototoxic activity was measured by means of a biological assay. The substances producing phototoxicity were identified by high-performance liquid chromatography as being oxypeucedanin and bergapten. The phototoxic potency of oxypeucedanin was only one-quarter of that of bergapten. However, the amounts of these two phototoxic compounds present in lemon oils produced in different regions of the world varied by a factor of more than 20 (bergapten, 4-87 ppm; oxypeucedanin, 26-728 ppm), and their ratio was not constant. The two compounds accounted for essentially all of the phototoxic activity of all lemon-oil samples. Among various other citrus-essential oils investigated, lime oil and bitter-orange oil also contained large amounts of oxypeucedanin. Oxypeucedanin was found to elicit photopigmentation on colored-guinea-pig skin without preceding visible erythema.
Eighty-one constituents were newly identified from the oil of Mentha piperita L ., including a new keto-alcohol, (-)-mintlactone and (+)-isomintlactone. They were determined by spectral data and syntheses to be 4-hydroxy-4-methyl-2-cyclohexen-lone (8), (6R, 7aR) (10) and (6R, 7aS)-3,6-dimethyl-5,6,7,7a-tetrahydro-2(4H)-benzofuranone (11) , respectively.
The reaction products of the title substances in hot acetic acid were separated by preparative TLC into compounds A–L according to the Rf-values, and the structural assignments for these products were now made as follows: A, 14H-[1,4]benzoxazino[3′,2′ : 3,4]cyclohepta[1,2-b][1,4]benzoxazine; B, 1-formylphenoxazine; F, cyclohepta[2,1-b : 2,3-b′]di[1,4]benzoxazine; G, cyclohepta[b][1,4]benzoxazin-10(11H)-one or its enolic form; J, cyclohepta[b][1,4]benzoxazin-6(11H)-one; L, 6-(o-hydroxyanilino)cyclohepta[b][1,4]benzoxazine hydrobromide. A small amount of 2-methylamino-3H-phenoxazin-3-one was also produced. Possible reaction pathways for the formation of these products are also discussed.
Cyclohepta[b][1,4]benzoxazine and 2-(o-hydroxyanilino)tropone were obtained by the reactions of 2-chloro- and 2-methoxytropone with o-aminophenol. A similar reaction with o-methoxylaniline gave 2-(o-methoxyanilino) tropone and 1-(o-methoxyanilino)-7-(o-methoxyphenylimino)-1,3,5-cycloheptatriene. The chemical and physical properties of cyclohepta[b][1,4]benzoxazine were discussed.
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