Aristolochic acid alkyl esters

Over the last seventy years over sixty species of Aristolochia have been exploited for chemical examination by research groups throughout the world and a variety of compounds have been isolated. The spectrum of physiologically-active metabolites from Aristolochia species covers 14 major groups based on structure aristolochic acid derivatives, aporphines, amides, benzylisoquinolines, isoquinolones, chlorophylls, terpenoids, lignans, biphenyl ethers, flavonoids, tetralones, benzenoids, steroids, and miscellaneous. The aristolochic acid derivatives, host of phenanthrene derived metabolites were further classified into aristolochic acids, sodium salts of aristolochic acids, aristolochic acid alkyl esters, sesqui- and diterpenoid esters of aristolochic acids, aristolactams, denitroaristolochic acids, and aristolactones. The terpenoids can further be subdivided into 4 groups mono-, sesqui-, di- and tetraterpenoids. 

Table 5 summarizes the occurrence of fourteen alkyl esters of aristolochic acids in Aristolochia species. It is noted that all the reported aristolochic acid alkyl esters are methyl esters except 32 which is an ethyl ester of aristolochic acid la with an ethoxy group at C-8 [129]. Compounds 25-31 are methyl esters of reported aristolochic acids whereas compounds 33-38 are methyl esters of non reported aristolochic acids. Among alkyl esters of aristolochic acids reported so far aristolochic acid I methylester (28) and aristolochic acid IV methylester (30) are frequently encountered in Aristolochia species. Formosan Aristolochia species are known to be rich source for alkyl esters of aristolochic acids, particularly A. zollingeriana [171,223] and A. cucurbitifolia [56,159]. 

Table 5. Aristolochic Acid Alkyl Esters Isolated from Aristolochia Species...

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