Phytochemistry on emsenn.net

Anthraquinone

Thu, 02 Apr 2026 00:00:00 +0000

Anthraquinones are a class of aromatic organic compounds based on the 9,10-anthracenedione skeleton — a tricyclic structure consisting of three fused six-membered rings with two ketone groups. They are produced by several plant families, most notably Polygonaceae (knotweed, rhubarb), Fabaceae (senna), Asphodelaceae (aloe), and Rhamnaceae (cascara sagrada).

Anthraquinones are the chemical basis of the oldest known class of laxative drugs. Senna, rhubarb root, cascara, and aloe have been used as purgatives across multiple medical traditions for millennia. The laxative mechanism is well characterized: anthraquinone glycosides pass through the small intestine unabsorbed, are hydrolyzed by colonic bacteria to release the active aglycone, which then stimulates colonic motility and inhibits water reabsorption — producing the cathartic effect.

Emodin

Thu, 02 Apr 2026 00:00:00 +0000

Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is a naturally occurring anthraquinone found in the roots and rhizomes of several medicinal plants, including Japanese knotweed (Reynoutria japonica), rhubarb (Rheum spp.), cascara sagrada (Frangula purshiana), senna (Senna alexandrina), and aloe (Aloe vera). It is one of the principal bioactive compounds in the Traditional Chinese Medicine herb Hu Zhang and in Da Huang (rhubarb root), where it contributes to their purgative and heat-clearing actions.

Traditional use

In TCM, emodin-containing herbs are classified as bitter and cold — herbs that drain heat, dry dampness, and promote downward movement (purgation). Rhubarb root (Da Huang) is the archetypal “drastic purgative” in the Chinese materia medica, used for constipation with heat signs, abdominal distension, and blood stasis. Japanese knotweed rhizome (Hu Zhang) shares these properties. The laxative action of both herbs is attributable primarily to their anthraquinone content, of which emodin is a major component.

Phytoalexin

Thu, 02 Apr 2026 00:00:00 +0000

A phytoalexin is a defensive compound that a plant synthesizes de novo in response to stress — pathogen infection, ultraviolet radiation, physical damage, or herbivore attack. Unlike constitutive defenses (compounds always present), phytoalexins are induced: the plant produces them only when threatened. The term was coined by Müller and Börger in 1940 from Greek phyton (plant) + alexein (to ward off).

Phytoalexins are typically low-molecular-weight antimicrobial compounds that accumulate at the site of infection, creating a localized chemical barrier against the invading pathogen. They belong to diverse chemical classes depending on the plant family: stilbenoids in Vitaceae (grapes) and Polygonaceae (knotweeds), isoflavonoids in Fabaceae (legumes), sesquiterpenes in Solanaceae (nightshades), indole derivatives in Brassicaceae (mustards).

Polyphenol

Thu, 02 Apr 2026 00:00:00 +0000

Polyphenols are a large and structurally diverse class of organic compounds produced by plants, characterized by the presence of multiple phenol groups — aromatic rings bearing hydroxyl (-OH) substituents. Over 8,000 polyphenolic compounds have been identified in plants. They are the most abundant antioxidants in the human diet, present in fruits, vegetables, tea, coffee, wine, chocolate, and medicinal herbs.

Plants produce polyphenols primarily as defensive compounds — protecting against ultraviolet radiation, pathogens, and herbivores. This defensive function is why stressed or damaged plants often produce higher concentrations of polyphenols than unstressed plants, and why phytoalexins (stress-induced defensive compounds) are frequently polyphenolic.

Resveratrol

Thu, 02 Apr 2026 00:00:00 +0000

Resveratrol (trans-3,5,4’-trihydroxystilbene) is a polyphenolic stilbenoid produced by plants as a phytoalexin — a defensive compound synthesized in response to injury, ultraviolet radiation, or fungal infection. It is found in grape skins, peanuts, blueberries, and most abundantly in the root and rhizome of Japanese knotweed (Reynoutria japonica), which produces resveratrol at concentrations 50–100 times higher than grape skins and is the primary commercial source for dietary supplements.

The French paradox

Resveratrol entered Western biomedical consciousness through the “French paradox” — the epidemiological observation, reported by Renaud and de Lorgeril in The Lancet in 1992, that French populations had lower rates of coronary heart disease than predicted by their saturated fat intake [@renaud1992]. Red wine consumption was proposed as the protective factor, and resveratrol — present in grape skins and therefore concentrated in red wine — was identified as a candidate molecule responsible for the cardioprotective effect. Whether resveratrol at the concentrations present in wine is sufficient to explain the epidemiological observation remains contested. The paradox may reflect dietary pattern effects (the Mediterranean diet), reporting artifacts, or multiple interacting factors rather than a single compound.

Stilbenoid

Thu, 02 Apr 2026 00:00:00 +0000

Stilbenoids are a class of polyphenolic compounds based on a 1,2-diphenylethylene (stilbene) backbone — two phenyl rings connected by a two-carbon ethylene bridge. They are produced by plants primarily as phytoalexins — defensive compounds synthesized in response to pathogen attack, UV radiation, or tissue injury. Stilbenoids are synthesized via the phenylpropanoid pathway from phenylalanine, with stilbene synthase catalyzing the final cyclization step.

Key stilbenoid compounds

Resveratrol (trans-3,5,4’-trihydroxystilbene): The most studied stilbenoid. Produced in large quantities by Japanese knotweed rhizome, grape skins, peanuts, and blueberries. Inhibits platelet aggregation, NF-κB, COX-2, and activates AMPK and SIRT1 pathways.