Plant and fungi 3,4-dihydroisocoumarins: Structures, biological activity, and taxonomic relationships

Isocoumarins are secondary metabolites of diversified distribution from plant to fungi and animal kingdom, showing interesting biological activities. Their analogues, 3,4-dihydroisocoumarins (DHICs), are a small group of derivatives of limited distribution. The structures of natural DHIC are extremely variable due to the different types of substitution in their basic skeleton and this variability influences deeply their biological activities. DHICs exhibit important biological and pharmacological properties such as antimicrobial, anticancer, insecticidal, antimalarial, and antioxidant activities. In particular, DHIC attract the attention for their bitter or sweet taste since some of them have a potent sweetening property, 400-800 times more potent than sucrose. Beside the beneficial effects of DHIC some of them have been investigated for their high toxicity, such as ochratoxin, and for their allergenic properties. Plants containing DHIC seem to be not systematically related, e.g., Aloe sp. (Xanthorrhoeaceae), Scorzonera sp., Crassocephalum sp. and Tragopogon sp. (Asteraceae), Xyris sp. (Xyridaceae), Daucus sp. and Notopterygium sp. (Apiaceae), Hydrangea sp. (Hydrangeaceae), Polygala sp. (Polygalaceae), Montrouziera sp. and Hypericum sp. (Guttiferae), Kigelia sp. (Bignoniaceae), and Haloxylon sp. (Chenopodiaceae). The aim of this review is to report the DHIC structures isolated in the last 30 years and to construct possible correlations between the species from a taxonomical point of view, outlining their biological propertie