Psoralens oxygenated

In the oxygen-independent Type III reactions the excited/sensi-tized psoralen donates its excitation energy directly to, or reacts with, the target compound. This occurs if the substrate and the target compound (e.g., DNA) are already in close proximity or intercalated. The reactions will proceed very rapidly via the excited singlet state, and are, typically, cyclization reactions or electron-transfer between the sensitizer and the target. In addition, the psoralen can be ionized, either directly or via the excited state, and react with the target compound in the form of a radical cation. Furocoumarins are also employed in treatment of cutaneous T-cell lymphoma and some infections connected with AIDS, by so-called photopheresis processes [71, 74-76]. In this case, peripheral blood is exposed to, e.g., photoactivated (sensitized) 8-methoxypsoralen (8-MOP) in an extracorporeal flow system. This... 

Oxygen-free reactions of psoralens, when in close proximity to the target, proceed via the first excited states in which the 3,4-and the 4, 5 7r-bonds of the pyrone and furan moieties, respectively, can undergo C4-cyclization reactions with, e.g., unsaturated bonds of lipids, or the C5=C6 double bonds of thymine in DNA. In reactions with DNA the psoralen is believed to intercalate with DNA in the dark. Subsequent irradiation at 400 nm usually leads to furan-side 4, 5 -monoadduct formation, whereas irradiation at 350 nm increases the formation of crosslinks in which the furan and pyrone rings form C4 cycloadducts to thymines on opposite strands [95], Subsequent irradiation of the 4, 5 -monoadducts at 350 nm leads to formation of crosslinks and conversion into pyrone-side 3,4-monoadducts. Shorter wave-... 

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). 

The MCI spectrum of psoralen (Fig. 9.25) indicates that resonance capture is occurring so that most of the ion current is carried hy the molecular ion at m/z 186. The associated GC trace indicates that ionisation is ca 10 times more efficient for the same amount of psoralen in comparison with El. In addition, since most of the ion current is channelled into the molecular ion, an analytical method which selectively monitored the molecular ion of psoralen would be ca 40 times more sensitive if NICI conditions were used rather than El. The technique only works for compounds which are electron capturing. The small ion at m/z 218 indicates that the psoralen has also formed an adduct with traces of oxygen present in the instrument, i.e. true chemical ionisation. 

Berdahl, D.R. and Wasserman, H.H. (1983) The reaction of psoralens and related benzofurans with singlet oxygen. An account of current research. Israel Journal of Chemistry, 23 (4), 409—414. 

Compositions of volatiles in different orange oils are shown in Tables 4 and 5. It is evident that most of the constituents belong to the terpene family and may be arranged into two groups, terpene hydrocarbons (terpenes and sesquiterpenes) and oxygenated terpene products (21). Aside from the volatile components, there are small amounts (2-15%) of nonvolatile residues in citrus peel oils that possess antioxidative property these include coumarins, psoralens, and polymethoxylated flavones (30-34). 

Psoralens, also known as furocoumarins, are naturally occurring or synthetic tricyclic aromatic compounds and are derived from the condensation of a coumarin nucleus with a furan ring [1-10]. Several new furocoumarins have been isolated from natural sources [10, llj. In addition, the synthetic methods for production of these molecules have been described and reviewed [10]. The synthetic methods can be organized on the basis of the key step used for the formation of the two different oxygenated rings, hi this respect, there are three possibilities (i) formation of the furan ring onto the coumarin, (ii) formation of the pyrone ring onto the benzofuran and... 

Alcohols. Boland and coworkers demonstrated conclusively that a P450 can catalyze the direct fragmentation of an alcohol into an olefin and a carbonyl-containing fragment . They studied the conversion of marmesin to psoralen in micro-somes derived from cell cultures of the plant Ammi majus (Figure 6.45) Deuterium labeled precursors allowed them to demonstrate that marmesin was converted into an equimolar mixture of acetone and psoralen, excluding the possibility of other oxygenated intermediates such as the known prandiol... 

Reaction (4) may follow after reaction (5), and reaction (2) may follow after reaction (6). Type I reactions may also be independent of oxygen, as is the case for the reactions of psoralens with DNA. 

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