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Silymarin is the phytochemical with medicinal properties extracted from Silybum marianum (L.) Gaertn. fruits. Yet, little information is available about silymarin biosynthesis. Moreover, the generally accepted pathway, formulated thus far, is not in agreement with actual experimental measurements on flavonolignan contents. The present work analyses flavonolignan and taxifolin content in 201 S. marianum samples taking into consideration a wide phenotypic variability. Two stable chemotypes were identified: one characterized by both high silychristin and silybin content (chemotype A) and another by a high silydianin content (chemotype B). Through the correlation analysis of samples divided according to chemotype, it was possible to construct a simplified silymarin biosynthetic pathway that is sufficiently versatile in explaining experimental results responding to the actually unresolved questions about this process. The proposed pathway highlights that three separate and equally sized metabolite pools exist, namely: diastereoisomers A (silybin A plus isosilybin A), diastereoisomers B (silybin B plus isosilybin B) and silychristin. In both A and B diastereoisomers pools, isosilybin A and isosilybin B always represent a given amount of the metabolite flux through the specific metabolite pool suggesting the possible involvement of dirigent protein-like enzymes. We suggest that chemotype B possesses a complete silymarin biosynthetic pathway in which silydianin biosynthesis is enzymatically controlled. On the contrary, chemotype A is probably a natural mutant unable to biosynthesize silydianin. The present simplified pathway for silymarin biosynthesis will constitute an important tool for the further understanding of the reactions that drive flavonolignan biosynthesis in S. marianum .

Tricin-type flavonolignans, (2S)-dihydrotricin 4'-O-(erythro-beta-guaiacylglyceryl) ether, (2S)-dihydrotricin 4'-O-(threo-beta-guaiacylglyceryl) ether, (2S)-dihydrotricin 4'-O-(threo-beta-4-hydroxyphenylglyceryl) ether, tricin 4'-O-(erythro-beta-4-hydroxyphenylglyceryl) ether, tricin 4'-O-(threo-beta-4-hydroxylphenylglyceryl) ether, and (2S)-dihydrotricin 4'-O-(beta-6''-methoxy-4''-oxo-chroman-3''-yloxy) ether namely calquiquelignan A-F, respectively, were isolated and characterized from the EtOAc extract of Calamus quiquesetinervius. Additionally, six known phenolic compounds, including dihydrotricin, tricin, salcolin A, p-hydroxybenzoic acid, (2S, 3S)-trans-dihydrokapempferol and (2S)-naringenin, were also obtained and identified from the extract. Structures of the flavonolignans were assigned based on spectroscopic analyses that included 1D and 2D NMR spectroscopic techniques, such as HMQC, HMBC, and NOESY. Bioassay results showed that calquiquelignan A, dihydrotricin and (2S)-naringenin exhibited significant vasodilatory potencies, as indicated by 60.3%, 80.3% and 60.9% relaxations, respectively, at 100 microM. Salcolin A showed potent platelet aggregation inhibition, compared with aspirin. Most of the tricin-type derivatives (calquiquelignan A-B, dihydrotricin and tricin) also exhibited more potent hydroxyl radical ((.)OH) scavenging activity than trolox as characterized by the ultraweak chemiluminescence assay.

Chemical examination of the n-BuOH extract from the aerial parts of Epimedium sagittatum led to isolation of three prenylated flavonol glycosides sagittasine A-C, two acylated flavonol glycosides kaempferol-3-O-(2''-E-p-coumaroyl,4''-Z-p-coumaroyl)-alpha-l-rhamnopyranoside and kaempferol-3-O-(3''-Z-p-coumaroyl,4''-E-p-coumaroyl)-alpha-l-rhamnopyranoside, together with known flavonoids, flavonolignans, 2-phenoxychromones, a lignan, and aromatic acid derivatives. Flavonolignans were identified for the first time in this plant. The vasorelaxing properties of the n-BuOH extract of E. sagittatum and 13 isolated compounds were tested using pre-contracted rat aorta rings in an organ bath apparatus. The results indicated that the n-BuOH extract of E. sagittatum produced a partial endothelial nitric oxide-dependent vasorelaxation, with EC(50) of 0.16+/-0.03 mg/ml. However, the 13 compounds tested, generated only a mild or moderate relaxation, and did not possess significant vasorelaxing effect individually.

Leaves of Hyparrhenia hirta yielded the rare diastereoisomeric flavonolignans tricin 4'-O-(erythro-beta-guaiacylglyceryl) ether and tricin 4'-O-(threo-beta-guaiacylglyceryl) ether together with their 7-O-glucosides, which are the first flavonolignan glycosides to be isolated as natural products. A complete set of (1)H and (13)C NMR resonance assignments obtained for both flavonolignan aglycones indicates the need for revision of data published previously for these compounds and for a reassessment of their original stereochemical designation.

Six flavonoids including two new flavones, luteolin 7-O-(4''-O-(E)-coumaroyl)-beta-glucopyranoside), chrysoeriol-7-O-(4''-O-(E)-coumaroyl)-beta-glucopyranoside) and a mixture of two pairs of diastereoisomeric flavonolignans, (+/-)-hydnocarpin 7-O-(4''-O-(E)-coumaroyl)-beta-glucopyranoside)/(+/-)-hydnocarpin-D 7-O-(4''-O-(E)-coumaroyl)-beta-glucopyranoside) with a 2:1 ratio were isolated from the whole plant of Mallotus metcalfianus Croizat, in addition to 10 known compounds. Their structures were evaluated on the basis of different spectroscopic methods, including extensive 1D and 2D NMR spectroscopy. Some extracts have moderate antimicrobial properties and interesting antiradical (DPPH) activity, as well as some compounds isolated from this species. Tannins were also identified in some active extracts.

Investigation of the leaves of Verbascum sinaiticum has afforded two flavonolignans, hydrocarpin and the novel sinaiticin, as well as two flavones, chrysoeriol and luteolin. All compounds exhibited dose-dependent cytotoxicity when tested against cultured P-388 cells.

The aerial parts of Onopordon corymbosum afforded seven flavonoids, 3-(3,4-dihydroxyphenyl)-1-propanol and two flavonolignans, hydnocarpin and the new 5′'-methoxy-hydnocarpin.