Coumarins angular furanocoumarins

Figure 4.3 Structures of coumarins, linear furanocoumarins and angular furanocoumarins.

Sardari, S., Mori, Y., Horita, K., Micetich, R.G., Nishibe, S. and Daneshtalab, M. (1999) Synthesis and antifungal activity of coumarins and angular furanocoumarins. Bioorg. Med. Chem., 7,1933-40. 

Another possibility of producing explicable signal displacements is the addition of complexing reagents. Bose et al. (41) reported that titanium tetrachloride in deuteriochloroform can be used as a shift reagent in H and l3C NMR spectroscopy, and applied this method to coumarin and some angular furanocoumarins (42). 

Table 10. 13C chemical shifts of linear (F) and angular furanocoumarins (H), their 2",3 -dihydro derivatives (G and I) and of coumarins with other... 

Effects of UV irradiation in the presence of furano-coumarins have also been studied with proteins, especially enzymes, and it is now clear that photobinding effects are not confined to nucleic acids. Both linear and angular furanocoumarins bind covalently to proteins in reactions highly dependent on structure. Enzymes are significantly inactivated, as shown in Table 1. The linear isomers appear generally to be most inhibitory, but there is great variation with the structure of both the coumarin and the protein. 

Most other reviews have classified coumarins in an arbitrary manner according to whether, for example, particular compounds were derivatives of linear or angular furanocoumarins or pyranocoumarins. In compiling the Tables included in the present review a biogenetically related approach has been adopted which is based firstly upon the number of nuclear oxygen atoms. Within each Table, the entries are presented in the following order — (i) coumarins with acyclic substituents, (ii) dihydrofuranocoumarins, (iii) furanocoumarins, (iv) dihydro-... 

Coumarins are widely distributed in the plant kingdom, especially in the families Apiaceae, Rutaceae, Leguminosae, and Compositae [30,31]. Generally, the highest level of coumarins is found in the fruits, followed by roots, stems, and leaves. In Table 1 are shown the main linear furanocoumarins present in the plant kingdom and vegetable sources. On the other hand, in Table 2 are shown the main angular furanocoumarins and their presence in different plants. 

After the separation of furanocoumarin, spectroscopic methods can be used to identify and quantify these phenolic compounds. Coumarin shows absorption bands at 274 and 311 nm, which have been attributed to the benzene and pyrone rings, respectively. Methyl substitution at C-5, C-7, or C-8 leads to a bathochromic shift of the 274 nm maximum but leaves the 311 nm maximum practically unchanged [68]. 7-Oxygenated coumarins show strong absorption bands at about 217 and 315-330 run with weak peaks or shoulders at 240-250 nm. Linear furanocoumarins show four zones of absorption at 205-225, 240-255, 260-270, and 298-316 nm. Angular furanocoumarins can readily be distinguished from linear forms since the maxima at 242-245 and 260-270 are absent [69]. 

Furanocoumarins are formed when furor ring is joined with coumarins. The plants of Rutaceae, Leguminosae and Apiaceae are rich sources of furanocoumarins. Depending upon the structure, the furanocoumarins are divided into linear and angular types. Furanocoumarin containing preparations are used externally as well as internally for treatment of leucoderma, psoriasis and skin carcinoma. 

Coumarins are lactones with the basic structure of 1,2-benzopyrone. Biosynthetically, they are mainly originated from shikimic acid padiway, with the intermediate of cinnamic acid. By the addition of a furan ring, the furanocoumarins are resulted, which are represented by psoralen (linear) and angelicin (angular) [10]. 

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