Terpenoids iridoids

Introduction of Nitrogen into a Terpenoid Skeleton. The acetate-derived fragments (35) mevalonic acid (30), which yields isopentenyl pyrophosphate (31) and its isomer, 3,3-dimethyl ally pyrophosphate (32) a dimeric C -fragment, geranyl pyrophosphate (33), which gives rise to the iridoid loganin (34) and the trimer famesyl pyrophosphate (35), which is also considered the precursor to C q steroids, have already been mentioned (see Table 3... 

Jensen, S.R., Plant iridoids, their biosynthesis and distribution in angiosperms, in Ecological Chemistry and Biochemistry of Plant Terpenoids, Harbome, J.B. et al., Eds., Clarendon Press, Oxford, 1991, 133. 

Magnolio- phyta (Ang.)> 250,000/50 Goom. 1992 Land ALKAL. benzyl phenylethyl, benzyltetraisoquinoline, indolizinoquinoline, phenethylamine, phenethylisoquinoline, terpenoid (secoloeanin). ISOPR. Monotem. iridoids Tritem. oleane hi high... 

Of biochemical interest is the presence of quite significant amounts (up to 5%) of the iridoid glycoside loganin (see page 188) in the fruit pulp of Strychnos nux-vomica. This compound is, of course, an intermediate in the biosynthesis of strychnine and other terpenoid indole alkaloids. 

All terpenoid indole alkaloids are derived from tryptophan and the iridoid terpene secologanin (Fig. 2b). Tryptophan decarboxylase, a pyridoxal-dependent enzyme, converts tryptophan to tryptamine (62, 63). The enzyme strictosidine synthase catalyzes a stereoselective Pictet-Spengler condensation between tryptamine and secologanin to yield strictosidine. Strictosidine synthase (64) has been cloned from the plants C. roseus (65), Rauwolfla serpentine (66), and, recently, Ophiorrhiza pumila (67). A crystal structure of strictosidine synthase from R. serpentina has been reported (68, 69), and the substrate specificity of the enzyme can be modulated (70). 

Lippia alba (Mill.) N.E. Br. - cidreira, erva-cidreira, melissa, carmelitana A calming effect, to relax, tranquilizer Leaves (decoction) Afro-Brazilians [3,41] Xukuru Indians [37] Caboclos [52,56,59] Ouilombolas [48] Alkaloids [219] saponins [220] sterols, flavonoids [221] essential oils [222,223] prenylated naphtoquinones [224] iridoids [225] terpenoids [226,227] phenolic acids [228] ... 

Only a few examples for alkaloids of terpenoid origin have been identified from arthropods. The ant Mommorium fiddi was shown to contain (2 ) and (2 2)-farnesylamine (148), which, surprisingly, constitutes the first identification of farnesylamine or any ofits derivatives in nature. The defensive agent actinidine (16) has been found in a number of insect species and probably derives from an iridoid precursor, although the details of actinidine biosynthesis in insects have not yet been fully clarified." ... 

Occasionally, plant alkaloids of terpenoid origin are sequestered by insects. For example, larvae of many species of sawfly are chemically protected by toxic metabolites they sequester from their host plants. This includes iridoid glycosides (see Section 2.04.3) and a group of steroidal alkaloids produced by plants of the genus Veratrum, such as zygadenine (149). In some cases, sawfly larvae have been shown to further metabolize sequestered Veratrum alkaloids for example, zygadenine is derived from hydrolysis of the ester functionalities in sequestered protoveratrine A (150). ... 

The basic structure of TIAs includes an indole nucleus derived from tryptamine, the decarboxylation product of the aminoacid tryptophan, and a versatile C9 or CIO terpenoid unit arising from the iridoid glucoside secologanin, Fig. (4). 

Secologanin (1) of Fig. (1) is the most important representative of the iridoids (la), a special type of cyclopentanoid monoterpenes. (1) belongs the subclass of secoiridoids (lb), in which the bond C-7-C-8 is cleaved [1]. The number of known iridoids is more than 650 [2], The biosynthesis of iridoids like that of other monoterpenes starts from two C5 units (lc) whose precursor was considered to be mevalolactone [3], However, recently it was proved that the biosynthesis of some classes of terpenoids [4,5], and specially of secologanin [6] runned from 1-deoxy-D-xylulose-5-phosphate as an alternative or even main route. 

Apart from rare terpenoid monoeyelie eyelopentane derivatives sueh as l-aeetyl-4-isopropenyleyelopentene from Eucalyptus globulus (Myrtaeeae), about 200 eyelopentane monoterpenes oeeur as iridoides and seco-iridoides. 4,7-Dimethyleyelo-penta[c]pyran ineorporates the basie skeleton of iridoids, while the C-6-C-7 bond of the eyelopentane rings opens in the seeo-iridoids. 

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