Chemosystematics

This study of Phlox Carolina represents one of the best examples in the flavonoid chemosystematic literature where workers combined thorough sampling, detailed statistical analysis, and an intimate knowledge of the biology of the system under scrutiny to produce a convincing picture of natural variation. As mentioned at the beginning of this discussion, a more casual approach would have undoubtedly overlooked the subtle differences that characterize this system. 

Cope, E. A. 1983. Chemosystematic affinities of a California population of Abies lasiocarpa. Madrono 30 110-114. 

Chemosystematics and ecology of lichen-forming fungi. Ann. Rev. Ecol. Syst. 

Mathela, C. S., Melkani, A. B., Pant, A. and Pande, C. 1988. Chemical variations in Cymbopogon distans and their chemosystematic implications. Biochem. Syst. Ecol. 16 161-165. 

Ptarmica chemosystematics of A. moschata and related species (Compositae—Anthemideae). Biochem. Syst. Ecol. 29 149-159. 

Volatade leaf oil analysis in chemosystematic studies of North American conifers. 

Harbome, J. B., Turner, B. L. Plant Chemosystematics. Academic Press, Orlando, FL, 1984. 

In Australian tenebrionid beetles, defensive compounds and their patterns seem to be of only low chemotaxonomic value. However, the aforementioned aromatic compounds are restricted to the genus Tribolium. Abdominal defensive compounds were used as chemosystematic characters in order to construct a phylogenetic tree for the genus Tribolium [330]. The defensive secretion of adults of Tenebrio molitor was shown to contain toluquinone 7 and m-cresol 89 [333]. The quantification of benzoquinones in single individuals of Tribolium castaneum at different days after adult eclosion indicates that the amount of toxic quinone only shows a maximum subsequent to cuticle sclerotization. Obviously, there is a need for an adequate cuticular barrier for self-protection from these defensive compounds [334]. 

Otto A, Wilde V, Sesqui-, di- and triterpenoids as chemosystematic markers in extant conifers. Botanical Review 67 141-238, 2001. 

Flavonoid analyses are mostly concentrating on plants which are of either pharmaceutical interest or of commercial value. In addition, flavonoids are important factors in biological interactions between living organisms. This is best illustrated by the last review Advances in flavonoid research since 1992 focusing on these topics. In contrast, mere distribution studies or chemosystematically oriented compilations are rare (e.g., on Asteraceae). Naturally, the presently known distribution of flavones and flavonols in plants reflects the current scientific interests, and hence the interpretation of their chemodiversity must be made with caution. 

In contrast to the numerous reports on flavones in Lamiaceae, only very few genera were found to accumulate flavonols in their exudates. The accumulation of 5,6-di-O-methylated derivatives in species of Salvia may be of chemosystematic significance, in relation to other... 

Species of the genus Vellozia have been extensively studied for their flavonoid complement in relation to chemosystematics. In addition to a series of C-methylflavonols and two C-prenylated flavonols, derivatives of vellokaempferol and velloquercetin are accumulated in whole plants, leaves, and leaf exudates. The basic structure of these compounds is characterized by 7,6-isopropenylfurano substitution, based upon kaempferol, quercetin, and their 0-methyl ethers. In addition, 8-C-methyl derivatives of these compounds were also identified from leaves of V. stipitata " So far, species of this genus are the only reported sources of these compounds, which in parts have been proved to be accumulated externally. ° Structures are exemplified by Figure 12.10. 

By comparison, a series of mostly monoacylated flavonols is known to date and recent reports increased the number slightly. Four new products came from Pseudognaphalium robustum and Tanacetum microphyllum (both Asteraceae), and from Adina cordifolia (Rubia-ceae). A diacetylated compound (3,5-diacetyltambulin) was recently isolated from the bark of Zanthoxylum integrifoliolum (Rutaceae). Since most of the flavonols are monoacylated, the accumulation of quercetin tetraacetate in Adina cordifolia is a remarkable result. Altogether, the newly reported compounds occur scattered in the plant kingdom their occurrence is so far of little chemosystematic value. Aerial parts of Tanacetum microphyllum (Asteraceae) yielded a derivative, which is structurally not an ester. It is, indeed, a carbo-methoxy derivative of 6-hydroxyluteolin-4 -methyl ether (compound 34 in Table 12.5). No other flavonoid of this type is known so far. 

It might be of more value to check the substitution patterns for their chemosystematic significance, as had been done earlier in frequency analysis. According to current data, 6-substitution, both —OH and —OMe, appears to be more frequent than the corresponding 8-substitution in flavones. The number of their 6,8-diOMe derivatives is quite considerable though. By comparison, the number of the related 6,8-OH-flavones is restricted to a few compounds reported from natural sources (compounds 136, 222, 227, and 262 in Table 12.1). All of the other polyhydroxylated structures have so far not been found as natural products. A similar ratio between 6- and 8-substitution was found with the flavonols, but the number of naturally occurring 6,8-diOH flavonols is limited to two compounds only (compounds 239 and 289 in Table 12.2). Further accumulation trends of possible chemosystematic relevance have been discussed in the respective sections. 

Valant-Vetschera, K.M., Eischer, R., and Wollenweber, E., Exudate flavonoids in species of Artemisia (Asteraceae-Anthemideae) new results and chemosystematic interpretation, Biochem. Syst. EcoL, 31, 487, 2003. 

Kawashty, S.A. etal.. The chemosystematics of Egyptian Trigonella species, Biochem. Syst. Ecol, 26, 851, 1998. 

Grayer, R.J. et al., Leaf flavonoid glycosides as chemosystematic characters in Ocimum, Biochem. System. EcoL, 30, 327, 2002. 

Wyatt, R., Lanes, D.M., and Stoneburner, A., Chemosystematics of Mniaceae II. Flavonoids of Plagiomnium section Rosulata, Bryologist, 94, 443, 1991. 

From a chemosystematic point of view, it is interesting to note that prenylated flavonoids such as microfolione (56) have been found in a species of the family Ptaeroxylaceae, because the relationships of this family with other families were disputed in the past. Most taxonomists considered the Ptaeroxylaceae closely related to families in the order Rutales to which the Rutaceae and Meliaceae belong, whereas others considered it related to the Sapindaceae. Flavonoid chemistry supports a close relationship to the Rutaceae and Meliaceae, as iso-prenylated flavanones also occur in these families, e.g., 58 and 98 in Boronia coerulescens ssp. spinescens, the farnesyl-bearing 121 (Figure 15.3) in B. ramosa (Rutaceae)," and flowerine (59) and flowerone (60) in Azadirachta indica (Meliaceae). Microfolione is one of the few new flavanones for which the (2i )-configuration has been determined. 

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