Isoprenoid structures

An allylic silane of this type serves as a reagent for the introduction of isoprenoid structures.116... 

Isoprenoid structures for carotenoids, phytol, and other terpenes start biosynthetically from acetyl coenzyme A (89) with successive additions giving mevalonate, isopentyl pyrophosphate, geranyl pyrophosphate, farnesyl pyrophosphate (from which squalene and steroids arise), with further build-up to geranyl geranyl pyrophosphate, ultimately to a- and /3-carotenes, lutein, and violaxanthin and related compounds. Aromatic hydrocarbon nuclei are biosynthesized in many instances by the shikimic acid pathway (90). More complex polycyclic aromatic compounds are synthesized by other pathways in which naphthalene dimerization is an important step (91). 

Balaban, A.T., Barasch, M. and Marcus, S. (1980a). Computer Program for the Recognition of Standard Isoprenoid Structures. MATCH (Comm.Math.Comp.Chem.), 8,215-268. 

It is quite difficult to find accurate and detailed analyses of single isomers for branched alkanes with more than 10 C-atoms in the literature. Nevertheless, GC analysis of heavy naphtha, kerosene and light gasoils indicates the prevailing presence of isoprenoid structures characterized by an average probability of methyl substitution of about 0.20 (Altgelt and Boduszynski, 1994). 

The isoprenoid structure hypothesis corresponds to an average of three methyl substitutions along the carbon chain. By comparison, the equivalent H-abstraction reaction of the 2,6,10-tri-methyl-dodecane, with a regular tri-isoprene structure, becomes ... 

Marine macroalgae produce a wide variety of intriguing and diverse isoprenoid structures derived from C5 isoprene units, and many reports have been published on the ecological roles of these metabolites. Marine terpenoids are frequently found with halogenated functionalities and one or more rings, which can have important implications for their biological activities. Isoprenoid metabolites are derived via the classical mevalonate pathway or the more recently discovered deoxyxylulose phosphate pathway. Isoprenoids are... 

Cubitene (95), which was isolated from an East African termite soldier, Cubitermes umbratus, possesses an unusual twelve-membered ring. Its structure was determined by A-ray analysis. The irregular isoprenoid structure may be derived via a cembrene derivative or by coupling farnesyl pyrophosphate with dimethylallyl pyrophosphate to give an irregular diterpenoid directly. 

Polyterpenoids.— C N.m.r. has been used to investigate the structure of the C55 polyprenol moraprenol-11 (190) from leaves of Moms alba. The main component has the trans-trans-trans-cis-cis-cis-cis-cis-cis-cis-OH configuration. The monophosphate of this compound was prepared in 34% yield by treatment with o-phenylenephosphorochloridate. Biosynthetic studies have provided evidence for the formation of 2,3-dehydrodolichyl phosphate (191) as an intermediate in dolichyl phosphate (192) biosynthesis. Most of the members of a series of C2S—C40 acyclic hydrocarbons obtained from crude oil have isoprenoid or degraded isoprenoid structures. The mokupalides from a marine sponge have been shown to be hexaprenoids with structures (193)—(195). ... 

The most interesting new polyterpenoids are a series of C40 diols that form part of macrocyclic diglycerol tetraethers which constitute the major membrane lipids of the extremely thermo- and acido-philic bacterium Caldariella. These compounds, (196)—(200), which may be acyclic or may have from one to four isolated cyclopentane rings are formally dimers of C20 isoprenoid structures linked head-to-head rather than the conventional tail-to-tail linkage in, for example, carotenoids.The isoprenoid nature of these compounds has been shown by labelling. 

Bixin, present in Annatto, is an important natural colourant which is obtained commercially from Bixa orellana. It is unusual in not having a typical isoprenoid structure composed of multiples of the fundamental C5 unit. All trans diethyl norbixin has been synthesised readily from crocetindial (ref.55,p221) by the Wittig reaction with two moles of the phosphoran from the triphenylphosphonium salt of ethyl chloracetate as shown in Scheme 20. The natural product is the form in which the colourant is used. 

Terpenes are functional compounds with an isoprenoid structure, found in the essential oils of plants such as lemon grass, cherry, mandarin, and citronella. To utilize functional terpenes, especially in the pharmaceutical field, geraniol, famesol, geranylgeraniol, phytol, perillyl alcohol, myrtenol, and nerol were phosphatidylated, and their antiproliferative effects on cancer cells were investigated in vitro [52,53]. Among these seven compounds, phosphatidyl-monoterpenes showed a markedly antiproliferative effect on human prostate PC-3 and human leukemia HL-60 cells. 

Larter S. R., Solli H. and Douglas A. G. (1983) Phytol-containing melanoidins and their bearing on the fate of isoprenoid structures in sediments. Advancer in Organic Geochemistry 1981, pp. 513-523, Wiley, New York. 

Isoprenoids (isopentenoids). The name for a group of natural products made up of isoprene units (e.g., ses-qui-, di-, and triterpenes, iridoids, carotinoids, steroids, natural rubber, etc.). Many non-isoprenoid compounds, however, do possess isoprenoid side chains, e.g., tocopherols, ubiquinones, chlorophyll, or contain isoprenoid structures incorporated into their skeletons, e.g., monoterpenoid indole alkaloids, penitrems, Cinchona alkaloids. 

Addition Reactions. The utility of ( )-phenylsulfonyl-2-tri-methylsilylethylene in the synthesis of a-substituted allylsilanes is exemplified in eq 3 for y-hydroxyvinylsilanes, and in eq 4 in the preparation of isoprenoid structures. In these reactions the reagent functions as a Michael acceptor, but a-lithiation may compete with less nucleophilic bases such as butyllithium. ... 

Because of their non-isoprenoid structure, the B. braunii dienes and trienes were expected to derive from fatty acids. This assumption was confirmed by feeding with [Ib- C] palmitic, [18- " C] stearic and [10-oleic acids, followed by analysis of the labelled hydrocarbons (27). In addition, the substantially higher incorporation level observed with oleic acid compared with incorporation in the saturated acids as well as the existence of a cis C(co9)-C(colO) double bond both in the major hydrocarbons produced by the tested strains and in oleic acid suggested that the latter is the direct precursor of these hydrocarbons. The inverse relationship existing between oleic acid and the hydrocarbon abundances supported this assumption indeed the oleic acid content of the algae remained low as long as hydrocarbon production was high, but rose considerably when hydrocarbon production sharply decreased. 

An allylic silane which serves as a reagent for introduction of isoprenoid structures has been developed. ... 

The synthesis of eight frame-shifted farnesyl diphosphate (FPP) analogues (17), bearing increased or decreased methylene units between the double bonds and/or diphosphate moieties of the isoprenoid structure, have been developed by Gibbs et al. Evaluation against mammalian... 

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