Valerian root consists of the dried underground parts of Valeriana officinalis (Valerianaceae), a perennial herb found throughout Europe. Drug material comes from wild and cultivated plants, and is carefully dried at low temperature (less than 40 °C) to minimize decomposition of constituents. Valerian preparations are widely used as herbal tranquillizers to relieve nervous tension, anxiety, and insomnia. Valerian was especially popular during the First World War, when it was used to treat shell-shock. The drug does possess mild sedative and tranquillizing properties, but for maximum activity the roots need to be freshly harvested and carefully dried. The major active principles are generally held to be a number of epoxyiridoid esters called valepotriates (0.5-1.6%), the principal component of which is valtrate (about 80%) (Figure 5.24). Minor valepotriates have the same parent iridoid alcohol as valtrate, but differ with respect to esterifying acids, e.g. isovaltrate (Figure 5.24), or are based on the reduced iridoid seen in didrovaltrate, again with various ester functionalities. Acid entities characterized in this group of compounds are mainly isovaleric (3-methylbutyric) and acetic (as in valtrate/isovaltrate/didrovaltrate), though more complex diester groups involving 3-acetoxyisovaleric and isovaleroxyisovaleric acids are encountered. During drying and storage, some of the valepotriate content may decompose by hydrolysis to liberate quantities of isovaleric acid, giving a characteristic odour, and structures such as baldrinal (Figure 5.24) (from valtrate) and homobaldrinal (from isovaltrate). Samples of old or poorly prepared valerian may contain negligible amounts of valepotriates. Standardized mixtures of valepotriates, containing didrovaltrate (80%), valtrate (15%), and acevaltrate (Figure 5.24) (5%), are available in some countries. These materials are usually extracted from the roots of other species of Valeriana, which produce higher amounts of valepotriates than V. officinalis, e.g. V. mexicana contains up to about 8%. Some other species of Valeriana that contain similar valepotriate constituents are used medicinally, including V. wallichi (Indian valerian) and V. edulis (Mexican valerian).
Despite the information given above, many workers believe the sedative activity of valerian cannot be due to the valepotriates, which are very unstable and not water soluble. Some of the sedative activity is said to arise from sesquiterpene derivatives such as valerenic acid (about 0.3%) and those constituting the volatile oil content (0.5-1.3%), e.g. valeranone (Figure 5.24), which have been shown to be physiologically active. GABA (y-aminobutyric acid) and glutamine have also been identified in aqueous extracts of valerian, and these have been suggested to contribute to the sedative properties. Small amounts of some iridoid-related alkaloids (Figure 5.24) have been isolated from valerian root (see page 386). The valepotriates valtrate and didrovaltrate are reported to be cytotoxic in vitro, and this may restrict future use of valerian. The reactive epoxide group is likely to be responsible for these cytotoxic properties.
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