Iridoid precursor

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." ... 

Elicitation Growth Regulators Heavy Metals Light Osmotic Stress Addition of Iridoid Precursors Induction Medium ... 

The feeding of loganin or secologanin to cells of C. roseus resulted in an increased alkaloid production (ajmalicine and strictosidine) and a decrease of the tryptamine level (136). After elicitation, these cells showed an increase of tryptamine, but the feeding of the iridoid precursors did not result in any further increase of alkaloid accumulation rather, a decrease was observed. Strictosidine was rapidly depleted from the cells after elicitation. 

Damtoft S, Franzyk H, Jensen SR (1995) Biosynthesis of iridoids in Syringa and Fraxinus carbocyclic iridoid precursors. Phytochemistry 40 785-792... 

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... 

It is well established that the iridoids are derived from two units of mevalonic acid (97), which itself is derived from acetyl-CoA. Mevalonate is also known to be a metabolic product of leucine (172), and the latter is a precursor of the monoterpene linalool (173). Wigfield and Wen (174) pursued the incorporation of leucine into the monoterpene unit in both vindoline (3) and catharanthine (4), where levels of 0.07 and 0.02%, respectively, were found, irrespective of the amount of precursor fed. This was important because, although initial results were obtained with [2- C] leucine, the specificity of incorporation was determined with 2- C-la-beled precursor. Two carbons in vindoline (3), C-8 and C-24, were en-... 

The other three classes of alkaloids arise from the complex iridoid tryptamine biogenetic pathway. The majority of the alkaloids which have been characterized from the Rubiaceae have the same early precursor. An alternative pathway, involving dopamine instead of tryptamine (16), leads to emetine-type alkaloids, which were found only in Cephaelis, a member of the tribe Psychotrieae. 

Strictosidine synthetase catalyzes the stereospecific condensation of trypt-amine and the iridoid glucoside secologanin to form strictosidine. The product is the precursor of the monoterpenoid-derived indole and quinoline alkaloids. 

Among the first synthetic achievements, based on the use of tricyclooctanones, are the following preparations of mono- and sesqui-terpenes. Four members of the monoterpene iridoid family have been obtained by a single approach (Scheme 17). The disadvantage of the stereo/io/iselective reduction of (21b), affording (82) and (83) in a 1 1 ratio, is compensated for by the benefit of simultaneous access to four natural products ( )-boschnialactone and the epimer (84), this being a suitable precursor to attain ( )-al-... 

The iridoid sesquiterpene (-)-specionin, an antifeedant to the spruce budworm, was synthesized by T. Hudlicky et al. using the low-temperature vinylcyclopropane-cyclopentene rearrangement as the key step. The substituted cyclopentenone precursor was first exposed to the lithium dienolate derived from ethyl 4-(dimethyl-fert-butylsilyloxy)-2-bromocrotonate at -110 °C to afford silyloxyvinylcyclopropanes as a mixture of exo and endo isomers (with respect to the vinyl group). The mixture was not separated but immediately subjected to TMSI/HMDS, and the corresponding tricyclic ketones were obtained in good yield. Similar results were obtained when TBAF in THF was used instead of TMSI. 

Vandewalle et al. have also used oxidative ring opening of one side of a norbomanone to prepare a number of iridoids, culminating in a synthesis and correction of the structure of specionin. At first they described the synthesis of teucrium lactone (425) and a loganin precursor (472) from the Diels-Alder adduct 473 of cyclopentadiene and methyl ( )-crotonate (Scheme 44). The same paper describes the preparation of the all-enafo-isomer 474 of ketone 475, from... 

Numerous synthetic applications of the inteimolecular Pauson-Khand reaction have been reported. Pauson has reported a number of very direct tqrplications of cycloadditions of ethylene in the synthesis of prostanoids and jasmone analogs (e.g. equations 15 and 16). - This is a reliable entry to 2-sub-stituted cyclopentenones. The suitability of cyclopentene and dihydrofuran as substrates has permitted the extension of this work to the preparation of still further varieties of prostaglandin analogs (e.g. equations 27 and 51). Simple 4,5-disubstituted 2-cyclopentenones are not as directly accessible, but may be prepared from the cycloaddition products of norbomadiene (equation 45). A sequence of conjugate addition followed by retro-Diels-Alder reaction affords the product (Scheme 5). Dihydrofuran cycloadditions have been used by Billington in the syntheses of the antibiotic methylenomycin B (Scheme 6), as well as cyclomethylenomycin A (synthetic precursor to the antibiotic methylenomycin A), cyclosarko-mycin (precursor to the antitumor agent sarkomycin) ° and the iridoid Jq>anese hop ether. ... 

Trost has used a,a-disulfenylated lactones as enolate precursors. As shown in equation (23), a,a-di-(phenylthio)- v-butyrolactone is treated sequentially with ethylmagnesium bromide and acetaldehyde to obtain -hydroxy lactone (8) in virtually quantitative yield. Oxidation of the phenylthio group and subsequent elimination of the resulting sulfoxide provides the unsaturated hydroxy lactone (9). The process was employed with more complex lactones in a total synthesis of iridoids. The method fails with a,a-di-sulfenylated ketones unless a catalytic amount of copper(I) bromide is included in the reaction mixture. 

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