Distribution of Bibenzyls, Prenyl Bibenzyls, Bis-bibenzyls, and Terpenoids in the Liverwort Genus Radula Abstract
Plants of the Radula genus are chemically very distinct from the other liverworts since they mainly elaborate bibenzyls including bibenzyl cannabinoids and prenyl bibenzyl derivatives, as well as bis-bibenzyls. Several of these components show biological activities such as psychoactivity, vasopressin antagonist, antimicrobial, antifungal, and NO production inhibitory activity, and cytotoxic activity against human cancer cell lines. While distribution of terpenoids in Radula species is in general very limited, some Portuguese species are rich sources of sesquiterpenoids. Among 679 liverwort species so far examined chemically, 264 species contained α-tocopherol, which may play an important antioxidative role for the constituents of oil bodies of liverworts
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One of the characteristic features of the genus Radula is the presence of bibenzyl cannabinoids in some of the species. The first example of the existence of such kind of compounds was the isolation of cis-perrottetinene (97) and perrottetinenic acid (98) from the New Zealand R. marginata Taylor.(6c) The Japanese R. perrottetii,(6b)R. campanigera, and R. chinensis,(8) the Costa Rican R. laxiramea Steph.,(13) and a Peruvian unidentified species also contained cis-perrottetinene (97).(9) Surprisingly, perrottetinenic acid (98) was isolated from the Japanese liverwort, Plagiochila ovalifolia Mitt., belonging to the Plagiochilaceae.(19)The discovery of these bibenzyl cannabinoids (97 and 98) has attracted the attention of organic chemists, biochemists, and pharmacologists. Chicca et al.(20) published the review article entitled “Uncovering the Psychoactivity of a Cannabinoid from Liverworts Associated with a Legal High”. in which the stereoselective total synthesis of cis- and trans-perrottetinene (97) were described and their in vitro pharmacology and tetrahydrocannabinoid (THC) isomers on cannabinoid receptors and endocannabinoid-degrading enzymes and in vivo pharmacology of cis- and trans-perrottetinenes were reported in detail. Both diastereomers of 97 readily penetrated the brain and induced hypothermia catalepsy, hypolocomotion, and analgesia in a CB1 receptor-dependent manner in mice, and cis-isomer interacts with major brain receptors, showing a selective cannabinoid pharmacology. Thus, cis-perrottetinene (97) found in several Radula species is a psychoactive cannabinoid.Hussain et al.(21a, published two in-depth review articles entitled “Identification of Putative Precursor Genes for Biosynthesis of Cannabinoid-like Compounds in Radula marginata” and “Demystifying the Liverwort Radula marginata, a Critical Review” on its taxonomy, genetics, cannabinoid phytochemistry, and pharmacology. In these reviews, the authors detailed genetic and transcriptomic resources of R. marginata and pharmacological aspects of cis-perrottetinene as compared to Δ9-tetrahydrocannabinol. The reviews also included morphological aspects using colored pictures and electron microscopic features of R. marginata and its taxonomic, phytogeographic, physiological, anatomical, biosynthetic, symbiosis, and evolutionary aspects.