Phototoxic compound

A well-investigated group of potent phototoxic compounds are the/wra-nocoumarins (psoralens) (Fig. 11.16), compounds that are also used as fish poisons. Furocoumarins absorb ultraviolet at around 330 nm and are converted to triplet stages these, in turn, produce singlet oxygen that damages amino acids (Fig. 11.17). 

Table 19.1 Chemical structures of some phototoxic compounds used in the 3T3 NRU validation.

However, this is an example of an essential oil in which the minor components are of great significance it contains a furocoumarin called bergaptene (0.2-0.5%), which is a phototoxic compound and needs to be used with caution. Many oils have it removed and are called FCF (furocoumarin-free) oils, even though this is technically a rectification of the whole oil. This is discussed under safety in Chapter 8. The odour of this oil is also influenced by the presence of trace components guaienol, spathulenol, nerolidol, farnesol and (i-sinensal. Box 7.8 shows safety data for bergamot oil and Box 7.9 shows a material data safety sheet. 

Chemicals that are potentially capable of phototoxic action have been Isolated from more than 30 flowering plant families. Their occurrence among Important monocot and dlcot families is shown in Table 1. Most of the taxa represented in this table synthesize several types of photosensitizers. Members of the Asteraceae (sunflower family) and the Rutaceae (citrus family) for example synthesize the widest range of phototoxic compounds. Other families (e.g., Hypericaceae, Llliaceae, Moraceae and Orchidaceae) either lack or fail to express such biosynthetic diversity. Plants from these latter groups contain phototoxins derived from a single metabolic pathway. 

Various biosynthetic classes of phototoxic compounds have been isolated from over thirty plant families (5). Some plant families produce more than one type of phototoxin. Three different types of phototoxins have been isolated from the Apiaceae ( celery family), for example, and eight different types have been identified so far from the Rutaceae (citrus family). Among other families that contain phototoxins are the Asteraceae (sunflower family), Euphorbiaceae (spurge family), Fabaceae (pea family) and Moraceae (fig family) ( i). 

Izdatelstvo Academii Nauk SSSR, Leningrad (in Russian) Komissarenko NF, Levashova IG (1988) Phototoxic compounds of the genus Dictamnus. In Vtoraya Resp. Konf. Po Med. Bot. - Kiev (Proceedings of the 2nd Repuhcan conference on medicinal botany, Kiev), Nauka, Kiev, pp 258-259 (in Russian)... 

These furocoumarins are phototoxic compounds which cause phototoxic dermatitis. Many plants of the Apiaceae (Umbelliferae) and most of the Rutaceae contain 5-methoxypsoralen (bergapten) and 8-me-thoxypsoralen (xanthotoxin). Their spectra is in the UV-A range (300-360 nm). 

Daniels, Jr., F. A Simple Microbiological Method for Demonstrating Phototoxic Compounds. J. Invest. Dermatol. 44, 259 (1965). 

Kagan, J., R. Gabriel, and S.A. Reed Alpha-terthienyl, a Non-Photodynamic Phototoxic Compound. Photochem. Photobiol. 31, 465 (1980). 

---