Secoiridoids biosynthesis

Further work on secoiridoid biosynthesis has now shown, using [7,8- H2]-7-deoxyloganic acid, that the C-8 proton as well as the C-7 proton is retained in the sequence loganin secologanin (126)— morroniside (129) (cf. Vol. 3, p. 28) in Lonicera morrowii, Cornus officinalis, and Gentiana thunbergii ... 

Plants in the Comanae, Gentiananae, and Loasanae, in general, contain both normal iridoid monoterpenes and secoiridoids. Plants in the Lamianae contain not only many normal iridoid monoterpenes but also those in which C-11 is decarboxylated. They lack secoiridoids. Plants of the Ericanae do not exhibit a clear pattern. Iridoid compounds with 8-P-stereochemistry were assumed to derive from pathways associated with secoiridoid biosynthesis, whereas those with 8-a-stereochemistry were associated with the route involving C-11 decarboxylation (Jensen, 1991). Some exceptions... 

Rovellini, P., andN. Cortesi. Identification of three intermediates compounds in the biosynthesis of OE069 secoiridoids as oleoside-type in different anatomic parts of Olea europaea L. by HPLC-electrospray-mass spectrometry. Riv Ital Sostanze Grasse 1998 OE070... 

Cyclopentanes, Iridoids.—A very useful review of the biosynthesis of the known sweroside-, morroniside-, and oleuropein-type secoiridoid glucosides, together with the biosynthesis of alkaloidal glucosides which can be regarded as secoiridoid... 

Loganin is the intermediate that undergoes the ring opening reaction which leads to the formation of secoiridoids. This step occurs by a mechanism that remains to be elucidated and affords secologanin (31) as the precursor of all of the secoiridoids and consequently, of the indole alkaloids that incorporate this pattern [1, 2, 3]. General biosynthesis of iridoids is given in fig. 1. 

In this work, we want to keep the structures of the iridoids and secoiridoids which are present in Oleaceae, their biosynthesis and the biological activities, so far described, up to date. 

Many reviews have dealt with the distribution, structure, properties and biosynthesis of iridoids and secoiridoids [131-137] without distinguish between the biosynthetic pathway route. In our case, some of the most studied activities, as anti-inflammatory, antitumoral-chemopreventive, and protective by iridoids biosynthesized by route IIa, have been discussed. 

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. 

The biosynthesis of the terpenoid indole alkaloids in C. roseus has been studied extensively, but still the pathway has not yet been completely elucidated on the level of the intermediates. Particularly, the secoiridoid pathway, and the different pathways after strictosidine leading to, for example, tabersonine and catharanthine are not yet completely known. On the level of the enzymes, certain steps have now been quite well characterized, but others remain unknown. The conversion of loganin into secologanin is one of the intriguing unresolved problems, although it is not a rate-limiting step. Even possible intermediates and the chemical mechanism behind this conversion are not clear, despite quite extensive studies. 

Biosynthesis A. is formed from tryptamine and the monoterpene secologanin (see secoiridoids) via stric-tosidine, catalysed by ca. 10 known enzymes (see also figure under monoterpenoid indole alkaloids). 

Biosynthesis Very well known, the first example of a complete elucidation at the enzymatic level for a group of alkaloids. It proceeds from tryptamine and secolog-anin (see secoiridoids) via strictosidine, 4,21-dehy-drogeissoschizine, and cathenamine. 

Biosynthesis In plants the quinoline system can be formed by several different biogenetic routes (biochemical convergence). In the Cinchona alkaloids tryptophan acts as the precursor while simple quinolines, furoquinolines, and acridines originate from an-thranilic acid. The second biosynthetic parmer is often a hemiterpene (for furoquinolines) or an iridoid monoterpene (secologanin, see secoiridoids) for Cinchona alkaloids. 

Biosynthesis Dimerization of two caracurine-VIl molecules, monomeric indoles with a C9-secoiridoid unit from Strychnos species, followed by methylation and thus quatemization at the non-indole nitrogen atoms. 

The biosynthesis of many indole alkaloids can be discussed in terms of the tryptophan-derived moiety and the non-tryptophan-derived moiety. Examples of non-tryptophan moieties include isoprene and secoiridoid units, polyketide moieties, and other amino acids. 

These chemical compounds are classified within the monoterpenoids, and are also known as secoiridoids. In the figure, the biosynthetic pathway from /-citronellal to sweroside, swertiamarin, and gentiopicroside is shown [9]. The study of the biosynthetic pathway was carried out using S.japon-ica or Gentiana triflora, and it was shown that gentiopicroside was derived from sweroside via swertiamarin. The structure elucidation, synthesis, and biosynthesis of the monoterpenoid alkaloids were reviewed by Cordell [10,11],... 

Thus, contrary to earlier expectations, various routes leading to the iridane skeleton in the biosynthesis of iridoids and secoiridoids are not identical (Inouye and Uesato, 1986). 

Contents L. Jaenicke and F.-J. Marner The Irones and Their Precursors. — M. Lounasmaa and P. Somersalo The Condylocarpine Group of Indole Alkaloids. — U. Sequin The Antibiotics of the Pluramycin Group (4//-Anthra [l,2- ]pyran Antibiotics). — R. M. Wenger Cyclosporine and Analogues — Isolation and Synthesis — Mechanism of Action and Structural Requirements for Pharmacological Activity. — H. Inouye and S. Uesato Biosynthesis of Iridoids and Secoiridoids. 

Biosynthesis characterization chemistry classification iridoids pharmacology secoiridoids synthesis... 

Coscia CJ, Botta L, Guamaccia R (1970) On the mechanism of iridoid and secoiridoid monoterpene biosynthesis. Arch Biochem Biophys 136 498-506... 

Damtoft S et al (1993) Biosynthesis of secoiridoid glucosides in Oleaceae. Phytochemistry 34 1291-1299... 

Inouye H et al (1971) Biosynthesis of oleuropein-type secoiridoid glucosides by oleaceae. Tetrahedron Lett 43 4073-4076... 

Obied H et al (2008) Biosynthesis and biotransformations of phenol-conjugated oleosidic secoiridoids from Olea europaea L. Nat Prod Rep 25 1167-1179... 

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