Terpenoids cyclic

Open-chain 1,5-polyenes (e.g. squalene) and some oxygenated derivatives are the biochemical precursors of cyclic terpenoids (e.g. steroids, carotenoids). The enzymic cyclization of squalene 2,3-oxide, which has one chiral carbon atom, to produce lanosterol introduces seven chiral centres in one totally stereoselective reaction. As a result, organic chemists have tried to ascertain, whether squalene or related olefinic systems could be induced to undergo similar stereoselective cyclizations in the absence of enzymes (W.S. Johnson, 1968, 1976). 

Simoneit, B.R.T., Grimalt, J.O., Wang, T.G., Cox, R.E., Hatcher, P.G. and Nissenbaum, A. (1986). Cyclic terpenoids of contemporary resinous plant detritus and of fossil woods, ambers and coals. Organic Geochemistry 10 877-889. 

Bloch therefore suggested isoprene units could be condensed first to give squalene and then cholesterol, an extension of Ruzicka s isoprene rule for the biosynthesis of linear and cyclic terpenoids. It was then necessary to show that selectively labeled 14C-acetate could get incorporated into squalene with the correct distribution of 14C and that this squalene could give rise to cholesterol, also with the appropriate position of the 14C label. 

Fig. 5 Cyclic terpenoid ethers identified in the interdigital secretion of the red hartebeest...

The formation of cyclic terpenoids involves intramolecular electrophilic addition, and this can be exemplified by the following monoterpene structures, again with all reactions being enzyme controlled. 

Many natural products, i.e. homologous aliphatic (lipids), polar (sugars, amino acids), and cyclic (terpenoids) compounds can be utilized as biomarkers. The following is a brief overview of the classical biomarkers commonly used, namely lipids and terpenoids. 

Simoneit BRT, Cyclic terpenoids of the geosphere, in Johns RB. (ed.), Biological Markers in the Sedimentary Record, Elsevier, Amsterdam, pp. 43—99, 1986. 

The Cl 3 ketones a- and /3-ionone are cyclic terpenoids that occur in many essential oils. However, being metabolites of the corresponding carotenoids [89], they occur in only small amounts. A third isomer, 7-ionone, has not yet been observed in nature. 

In addition to cyclic terpenoids, several other cycloaliphatic compounds have above-average importance as fragrance materials some of them are structurally related to the terpenes. 

The bushes grow wild and are cultivated in South Africa. The major components of the oils are (+)-limonene (ca. 10%) and other cyclic terpenoids that are structurally related to menthone. However, the constituents responsible for the... 

Chlorocyclopropylidenacetates are versatile starting materials in the synthesis of cyclic terpenoid systems255. In the methyl ester (154), the two independent molecules lie in mirror planes in the orthorhombic Pnma crystal, thus the heavy-atom skeletons are completely planar255. The distal bond, 1.548 (8) A, and the vicinal bonds, 1.453 (7), 1.457 (7) A, have the same lengths as in 142 the C=C bond is shortened to 1.311 (7) A. Reactivity in Diels-Alder and Michael additions cannot be directly deduced from the geometrical features. 

The rest of the cyclic terpenoid sulfides are complex mixtures of partially degraded and isomerized derivatives of the terpenoid sulfides which elute on the capillary GC column as a broad, unresolved hump. On Raney nickel reduction this fraction yields a complex mixture of naphthenic hydrocarbons which cannot be resolved further by GC analysis. 

A number of hydrocarbon fractions from liquefaction products produced at GFETC from the coals studied here were investigated using selected ion profiles of the capillary GC/MS data. None of the hydrocarbon biological markers other than the acyclic alkanes already discussed were detected. There were no sesquiterpenes, sesquiter-panes, steranes, triterpanes or other cyclic terpenoids found. 

The biogenesis of many cyclic terpenoids requires a cts-double bond in the acyclic precursor. A cis-double bond is frequently incorporated into the terminal isoprenoid unit via an allylic rearrangement mechanism. Alternatively, a cis unit could be incorporated directly (as rubber). Two results this year highlight some features of this problem. Both geraniol (22) and nerol (23) are derived from all-trans units (i.e. retention of the 4i -proton of mevalonate) so that the cis-double bond of nerol is derived by isomerization. The sesquiterpenoid gossypol (34) is derived from c/s,cis-farnesyl pyrophosphate. Hence in its biosynthesis either... 

Only the (-f )-enantiomer of this cyclic terpenoid is reduced to A -menthene... 

Circular Dichroism. The salicylidene-imino chirality rule has been applied to cyclic steroidal amines. This rule was previously used to correlate the absolute configuration of cyclic terpenoid amines with the signs of the observed Cotton effects near 255 and 315 nm in their circular dichroism spectra. Similar considerations were used to interpret the c.d. spectra of fV-salicylidene derivatives of steroidal cyclic amines. These spectra were reported but no simple interpretation was possible. 

The bushes grow wild and are cultivated in South Africa. The major components of the oils are (+)-limonene (ca. 10%) and other cyclic terpenoids that are structurally related to menthone. However, the constituents responsible for the characteristic blackcurrant odor are frans-8-mcrcapto-p-menthanc-3-one [34352-05-1] and its S-acetate derivative [57074-34-7] which are two of the small number of naturally occurring sulfur-containing terpenoids known to date [289, 290]. 

CYP71D subfamily is also large and currently comprises a total of 22 members from 10 different plant species. At present, the catalytic properties of five CYP71D enzymes have been determined and the enzymes assigned to specific steps in indole alkaloid, sequiterpenoid, cyclic terpenoid, and flavonoid synthesis. Accordingly, enzymes belonging to the CYP71D subfamily do not necessarily share similar functional characteristics. 

The phenanthrene and chrysene structures could be derived from cyclic terpenoids such as abietic acid, sterols, and hopanes (34). Although tri-phenylene, which has the highest resonance energy among the four-ring catacondensed PAHs (35), was not present in the SRC II HD at a significant level, this compound was found in the coal tar which is a higher temperature... 

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