Xanthotoxin linear furanocoumarin

CYP6D1 of the housefly (Musca domestica) has been found to hydroxylate cyper-methrin and thereby provide a resistance mechanism to this compound and other pyrethroids in this species (Scott et al. 1998 see also Chapter 12). Also, this insect P450 can metabolize plant toxins such as the linear furanocoumarins xanthotoxin and bergapten (Ma et al. 1994). This metabolic capability has been found in the lepi-dopteran Papilio polyxenes (black swallowtail), a species that feeds almost exclusively on plants containing furanocoumarins. 

Bull, D.L., Ivie, G.W., Beier, R.C., and Pryor, N.W., In vitro metabolism of a linear furanocoumarin (8-methoxypsoralen, xanthotoxin) by mixed-function oxidases of larvae of black swallowtail butterfly and fall army worm, /. Chem. Ecol., 12,885,1986. 

It has been shown that in insects cytochrome P450 monooxygenases are involved in metabolism of host plant allelochemicals by Lepidoptera larvae. Expression of the CYP6B1 alleles in lepidopteran cell lines has demonstrated that both P450 isoforms metabolize substantial amounts of linear furanocoumarins, such as xanthotoxin and bergapten, but not angular furanocoumarins, such as angelicin (4) and sphondin [249]. 

The furanocoumarins, psoralen, bergapten, xanthotoxin and isopimpinellin, were detected in celery leaves and stalk. The total furanocoumarin content ranged from about 12 to 50 mg/kg in Florida cultivars [54]. Treatment with fungicides increased the bergapten content 2-4 times in leaves and stalk, xanthotoxin 2-3 times in stalk, and isopimpinellin about 2-3 times in leaves, while psoralen levels remained constant. This fact is of some importance since linear furanocoumarins are the cause of photosensitive reactions in humans. 

Interestingly, the black swallowtail butterfly has maximized its metabolic detoxification processes allowing its larva to feed on plants with a high linear furanocoumarin content (40) Psoralen, bergapten, xanthotoxin, and isopimpinellin are... 

Psoralens in Healthy Celery. Healthy celery contains at least four linear furanocoumarins (Figure 1), psoralen, bergapten, xanthotoxin, and isopimpinellin (14). The observed quantities of linear furanocoumarins in healthy samples of three different celery cultivars grown at different locations in the U.S. are shown in Table I. 

During the measurement of linear furanocoumarins in fresh celery (14), relatively high levels of psoralens were randomly observed in some samples. It was then hypothesized that psoralens may function as phytoalexins in celery. The linear furanocoumarin, xanthotoxin, has been previously reported as being a phytoalexin in parsnip root (Pastnaca sativa) (24). 

Figure 6. HPLC tracings of the detector response vs. retention time for sodium hypochlorite-treated celery cv. 5270-R after 72 hat 2 °C and 26 °C in comparison to the linear furanocoumarin standards psoralen (p), bergapten (b), xanthotoxin (x), and isopimpinellin (i).

The first linear furanocoumarin to be isolated from parsley was bergapten (62). Later work provided quantitative data for bergapten, xanthotoxin, and isopimpinellin from dried parsley grown in greenhouse conditions (15). 

Coumarin biosynthesis involves formation of PAL and 4-coumarate CoA ligase which is light and elicitor inducible. Cells of P. crispum respond by producing the linear furanocoumarins psoralen (17), bergapten (18), and xanthotoxin (19) (Fig. 9.6), as well as other furanocoumarins (Ellis, 1988). The relative amounts of furanocoumarins in the mixture was changed by use of different fungal elicitor sources. 

Insect herbivory is an important selective force in the ecology and evolution of plants. The linear furanocoumarin, xanthotoxin (19), found in many plants of die Apiaceae and Rutaceae is toxic to the larvae of Spodoptera eridania, a generalist insect herbivore. This toxicity was shown to be increased in the presence of UV light. 

Butterflies of the genus Papilio (Lepidoptera) often are associated with members of the Apiaceae. Xanthotoxin (19), a linear furanocoumarin, occurs in many plants of the Apiaceae. This compound is not appreciably toxic to the larvae of Papilio polyxenes which normally feed on umbelliferous plants. Most of these insects feed only on plants that have linear furanocoumarins and, in general, do not consume plants that make angular furanocoumarins. Angelicin (30)... 

Linear furanocoumarins, such as psoralen, bergapten, xanthotoxin, and isopimpineUin isolated from three varieties of Apium graveolens, were examined by normal-phase HPLC equipped with a variable wavelength detector set at 250 nm [75]. 

A sensitive, specific, and rapid LC-MS method has been developed and validated for the simultaneous determination of xanthotoxin, psoralen, isoim-pinellin, and bergapten [80]. A paper by Zheng et al. [81] reported the quantitation of eleven coumarins including furocoumarins in Angelica dahurica, using HPLC-ESl-MS/MS. Yang et al. [82] developed a method for the characterization of linear furanocoumarins in Radix glehniae by LC-MS by the... 

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