Isoprenoid acids

Larcher, A. V., Alexander, R., Rowland, S. J. and Kagi, R. I. (1986) Acid catalysis of alkyl hydrogen exchange and configurational isomerisation reactions acyclic isoprenoid acids. Organic Geochemistry 10, 1015. 

First reported in recent marine sediments in 1967 275) have since been found in several marine basins 140, 141) Cooper and Blumer 140) suggested that the isoprenoid acids may provide markers for the contribution of animals lipids to the organic matter of recent sediments... 

Blumer, M., Cooper, W. J., Isoprenoid Acids in Recent Sediments, ... 

Cason, J., Graham, D. W., Isolation of Isoprenoid Acids From a Cali-... 

The peaks for C14 monounsaturated fatty acids follow 14 0 and are usually a jumble of peaks for 14 1 isomers, mixed up with those for iso and anteiso 15 0 and the isoprenoid 4,8,12-trimethyltridecanoic acid, followed reasonably clearly by that for 15 0 (Table 2). Little interest exists in these details, and the only obvious next peak before 16 0 should be iso-16 0, and sometimes another isoprenoid acid, pristanic or 2,6,10,14-tetramethylpentadecanoic, is found just ahead of 16 0. 

As already mentioned, isoprenoid acids were found only recently, in the same fraction of the weak acids in which hopanoic acids were identified. 

The finding of isoprenoid ketones and recently of a range of isoprenoid acids in the Aleksinac shale bitumen was of interest because isoprenoid acids had never been identified in the oxidation products of the corresponding kerogen (26,27) ... 

The second category of branched-chain FA consists of the isoprenoid acids, derived from isoprene nnits (see Section 3.5). They are widely distribnted in both terrestrial and marine organisms. Examples include 2,6,10,14-tetramethylpenta-decanoic acid (pristanic acid) and 3,7,11,15-tetramethylhexadecanoic acid (phytanic acid). 

The presence of polar or polarizable groups close to the chiral centre can promote hydrogen bonding or 7i-overlap with the stationary phase and enhance the resolution. This was again shown to be a significant structural feature in the separation of diastereomeric amides of acyclic isoprenoid acids [11]. The introduction of an olefinic group close to the chiral centre increased the separation factors. Similarly, separation factors were decreased... 

Isoprenoid acid [55, 74] Hydroxy carboxylic acids [75] Pyrethroid acids [58, 62, 76]... 

This class of fatty acids has the general formula of R-(CH2CH-CH3CH2CH2) -CH-C = CH-COOH, where R = H. These saturated and partially unsaturated multibranched fatty acids belong to the is-oprenoid acid family, and in nature, isoprenoid acids are often found in microorganisms and plants. Phytenic acid, whose systematic name is 3,7,11,15-tetramethyl-2-hexadecenoic acid (Figure 4), is one member of this class. 

Branched-chain acids, such as iso- (with an isopropyl terminal group) or anteiso- (a secondary butyl terminal group) are rarely found in food. Pristanic and phytanic acids have been detected in milk fat (Table 3.6). They are isoprenoid acids obtained from the degradation of the ph5dol side chain of chlorophyll. 

The carboxylic acid subfraction is essentially composed of n-C 2 to Cl8 even carbon numbered fatty acids, with palmitic acid as the major constituent (75). Isoprenoid acids (C14, C15, C17 and C19) were also detected in this subfraction the most abundant is the C15 acid (89). Such acids, whose structure was established by means of the fragmentation patterns in EIMS are rarely found in nature. 

D-Mevalonic acid is the fundamental intermediate in the biosynthesis of the terpenoids and steroids, together classed as poly-isoprenoids. The biogenetic isoprene unit is isopentenyl pyrophosphate which arises by enzymic decarboxylation-dehydration of mevalonic acid pyrophosphate. D-Mevalonic acid is almost quantitatively incorporated into cholesterol synthesized by rat liver homogenates. 

Isoprenoid compounds are biosynthesized from acetate by a process that involves sev eral stages The first stage is the formation of mevalonic acid from three molecules of acetic acid... 

In keeping with its biogenetic origin m three molecules of acetic acid mevalonic acid has six carbon atoms The conversion of mevalonate to isopentenyl pyrophosphate involves loss of the extra carbon as carbon dioxide First the alcohol hydroxyl groups of mevalonate are converted to phosphate ester functions—they are enzymatically phosphorylated with introduction of a simple phosphate at the tertiary site and a pyrophosphate at the primary site Decarboxylation m concert with loss of the terti ary phosphate introduces a carbon-carbon double bond and gives isopentenyl pyrophos phate the fundamental building block for formation of isoprenoid natural products... 

Vitamins are classified by their solubiUty characteristics iato fat-soluble and water-soluble groups. The fat-soluble vitamins A, E, and K result from the isoprenoid biosynthetic pathway. Vitamin A is derived by enzymic cleavage of the symmetrical C q beta-carotene, also known as pro-vitamin A. Vitamins E and K result from condensations of phytyldiphosphate (C2q) with aromatic components derived from shikimic acid. Vitamin D results from photochemical ring opening of 7-dehydrocholesterol, itself derived from squalene (C q). 

Fluorescein paraffin derivatives, waxes, hydrocarbons [140,141] aliphatic acids [142] hydroquinone and chlorinated derivatives [143] isoprenoids, quinones [111,144] oxathizine fungicides [145] barbiturates, phenothiazines [146]... 

Rhodamine 6G long-chain hydrocarbons [169] squalene, a-amyrin [170] methyl esters of fatty acids [171] glycerides [91] sterols [172, 173] isoprenoids, quinones [HI] lipoproteins [174] glycosphingolipids [175] phenolic lipids [176] phosphonolipids [177] increasing the sensitivity after exposure to iodine vapor [178,179]... 

The antiinflammatory effects of statins likely result from their ability to inhibit the formation of mevalonic acid. Downstream products of this molecule include not only the end product, cholesterol, but also several isoprenoid intermediates that covalently modify ( pre-nylate ) certain key intracellular signaling molecules. Statin treatment reduces leukocyte adhesion, accumulation of macrophages, MMPs, tissue factor, and other proinflammatory mediators. By acting on the MHC class II transactivator (CIITA), statins also interfere with antigen presentation and subsequent T-cell activation. Statin treatment can also limit platelet activation in some assays as well. All these results support the concept that in addition to their favorable effect on the lipid profile, statins can also exert an array of antiinflammatory and immunomodulatory actions. 

Isonicotinic acid hydrazide reagent 318 Isoprenaiine 395,396 Isoprenoid compounds 44 Isopulegol 59 Isoquercitrin 279, 280, 323 Isoquinoline alkaloids 46, 66, 262 Isorhamnetin 323 Isothiazolones, microbiocidal 45 Isothiocyanates 75 Isotopes, j8-radiation-emitting 41 -, detection limits 41 Itaconic acid 61... 

Since carotenoids are isoprenoids, they share a common early pathway with other biologically important isoprenoids such as sterols, gibberellins, phytol and the terpenoid quinones (Fig. 13.3). In all cases, these compounds are derived from the C5 isoprenoid, isopentenyl diphosphate (IPP). Until a few years ago it was believed that a single pathway from the Cg precursor mevalonic acid (MVA) formed IPP, which itself was synthesised from hydroxymethylglutaryl coenzyme A (HMG CoA) by the action of HMG... 

The isoprenoid side chains of quinones are biosynthesized mainly by the mevalonic acid pathway from acetyl-CoA. Another pathway to biosynthesizing isoprenoids is the so-called non-mevalonate ronte by which isopentenyldiphosphate (IPP) is formed from glyceraldehyde 3-phosphate and pyrnvate. The key molecule is the famesyl-diphosphate (FPP) that accepts other IPP molecules to form polyprenyl diphosphates. 

These topics are discussed in more detail in other chapters of this text. Formally, the pyrolytic elimination of sulphur dioxide from a sulphone, with the concomitant formation of a new carbon-carbon bond, constitutes a reduction at sulphur. These reductions have been valuable in the formation of new molecules, especially macrocycles and cyclophanes, and have been reviewed by Vdgtle and Rossa . Pyrolytic elimination of sulphur dioxide has been used by Julia and coworkers in the formation of mixtures of isoprenoids , and by Takayama and collaborators in the stereoselective synthesis of vitamin Dj 19-alkanoic acids . ... 

Suzuki, K. Application of mass spectrometry to bacterial taxonomy. Cellular fatty acids and isoprenoid quinones. Iyo Masu Kenkyukai Koenshu 1987,12,45-53. 

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