2- methyl farnesyl pyrophosphate

The substrate specificity of farnesyl pyrophosphate synthetase has been studied using 3-methyl-2-aIkenyl pyrophosphates (90) as models. When (90) bears a large side-chain i.e. R = C4H9), the reaction with isopentenyl pyrophosphate ceases after the formation of (91) and this reaction has been... 

Further detailed study of the substrate specificity of yeast squalene synthetase has been reported (see Vol. 7, p. 130). The enzyme is very sensitive to changes in substrate. For example, 10,11-dihydrofarnesyl pyrophosphate was converted into 2,3,22,23-tetrahydrosqualene with only 60% of the efficiency of farnesyl pyrophosphate whereas 6,7-dihydro- and 6,7,10,11-tetrahydro-farnesyl pyrophosphates were not metabolized. The first of the two binding sites has a greater preference for farnesyl pyrophosphate and this accounts for the formation of the unsymmetrical squalene product when mixtures of farnesyl pyrophosphate and a modified substrate are used. The importance of the methyl groups, especially that at C-3, for binding is emphasized by the low efficiency of conversion of 3-desmethylfarnesyl, , -3-methylundeca-2,6-dien-l-yl (1), and E,E-7-desmethylfarnesyl pyrophosphates. The prenylated cyclobutanones (2) and (3)... 

Menaquinone. The incorporation of [2- C]mevalonate and [2- C]-2-methyl-l,4-naphthoquinone into MK-4, normally considered a bacterial quinone, has been demonstrated in marine invertebrates such as crabs and starfish." Incorporation into 2,3-epoxy-MK-4 (163) was also observed. Cell-free extracts have been prepared from Escherichia coli which catalyse the conversion of o-succinylbenzoic acid (164) into l,4-dihydroxy-2-naphthoic acid (165) and menaquinones. In the presence of farnesyl pyrophosphate the major menaquinone produced was MK-3. Genetic studies with mutants of E. coli K12 that require (164) offer support for the generally accepted pathway for MK biosynthesis via (164) and (165)." The enzyme system that catalyses the attachment of the polyprenyl side-chain to 1,4-dihydroxy-2-naphthoic acid to form demethylmenaquinone-9 (166) has been isolated from E. colU ... 

Fig. 3.14. Farnesylation at the C-terminus. The signal sequence for farnesylation is the C-termi-nal sequence CAAX. In the first step a farnesyl moiety is transferred to the cystein in the CAAX sequence. The farnesyl donor is farnesyl pyrophosphate and the responsible enzyme is farnesyl transferase. Subsequently, the three C-terminal amino acids are cleaved (A alanine, X any amino acid) and the carboxyl group of the N-terminal Cys-residue becomes methylated.

At first glance, it is not at all clear that steroids are terpenoid in origin. The 5n numbers are absent— cholesterol is a C27 compound while the others variously have 20,21, or 23 carbon atoms. Studies with labelled mevalonic acid showed that cholesterol is terpenoid, and that it is formed from two molecules of farnesyl pyrophosphate (2 x C45 = C30 so three carbon atoms must be lost). Labelling of one or other of the methyl groups (two experiments combined in one diagram ) showed that two of the green carbon atoms and one of the black carbon atoms were lost during the biosynthesis. 

Several papers report new findings on ubiquinone biosynthesis. A mitochondrial membrane-rich preparation from baker s yeast can convert 4-hydroxybenzoate and isopentenyl pyrophosphate into the ubiquinone precursor 3-all-trans-hexaprenyl-4-hydroxybenzoate (234). Details of the cell-free system are presented. With preformed polyprenyl pyrophosphates, the system catalysed the polyprenylation of several aromatic compounds, e.g. methyl 4-hydroxybenzoate, 4-hydroxybenzaldehyde, 4-hydroxybenzyl alcohol, and 4-hydroxycinnamate. No evidence was obtained for the involvement of 4-hydr-oxybenzoyl-CoA or 4-hydroxybenzoyl-S-protein in the reaction. With shorter-chain prenyl pyrophosphates a shorter prenyl side-chain was introduced, e.g. geranyl and farnesyl pyrophosphates gave products with a 3-diprenyl and 3-triprenyl side-chain respectively. A crude enzyme preparation from E. coli... 

Fig. 3. Farnesylation and further processing of proteins containing a C-terminal CaaX-motif. Farnesyl transferase catalyses the transfer of a farnesyl moiety from farnesyl pyrophosphate FPP) to the cysteine residue in the CaaX-motif, where C = Cys, a = usually aliphatic amino acids, and X = Met, Ser Cys, Ala, Gin. The three C-terminal amino acids (aaX) are then cleaved off, and a methyl group is transferred from S-adenosyl methionine to the now C-terminal cysteine residue...

Humulene biosynthesis probably involves the intermediacy of a monocyclic carbonium ion or its biological equivalent [c/. (303)] derived from trans,trans-farnesyl pyrophosphate (16), A recent investigation based on this idea has shown that treatment of the ( , )-mesylate (303 Z=OMs) with dime thy laluminium phenoxide provides humulene (304) in excellent yield. The corresponding (Z, )-isomer, when treated with di-isobutylaluminium 2,6-dibutyl-4-methyl-phenoxide, is efficiently converted into germacrene (307) whereas the E,E)-isomer under these conditions provides a mixture (2 1) of humulene (304) and germacrene A (305). Monohydroboration-oxidation of caryophyllene... 

In an attempt to improve the inhibition kinetics, a pepticinnamin E library was synthesized to explore the chemical space of the natural product7 Three types of modifications were investigated changes to the N- and C-terminal substituents on the backbone, changes in N-methylation status, and the addition of an N-terminal histidine residue to form an interaction with the active site zinc atom. The inclusion of a histidine residue at the N-terminal peptide position proved favorable and modulation of the N-terminal substituent (i.e., the farnesyl pyrophosphate mimic) proved important for inhibition. Several of the compounds from the library were shown to induce apoptosis in MDCK-f3 tumor cells at concentrations of 100 pmol 1 however, in the case of only one compound could apoptosis be linked to FT inhibition. 

Given a sufficiently strong base, the activation produced by the phosphoryl group next to an adjacent C—H bond will allow deprotonation and the generation of a highly reactive carbanion. Butyllithium has been commonly used for this purpose, but a preference has been shown in recent work for Ida. Treatment of the anion from methyl methyl(4-morpholinyl)phosphinate (284) with farnesyl chloride yields 285, which, on acidolysis, affords the phosphonic acid 286, employed in the synthesis of a pyrophosphonate analogue of farnesyl pyrophosphate ". Alkylation of the carbanion from the chiral phosphonic diamide 287 (X = Me or higher alkyl) leads to the diastereoisomeric phosphonic... 

Syntheses of pyrophosphonate analogues of farnesyl pyrophosphate were achieved starting from methyl methylphosphonomorpholidate (232) and through the intermediate (235)(Scheme 24), ... 

Post-translational modification of Ras includes farnesylation, removal of the first 3 carboxyl-terminal amino acids, methyl esterification of the new carboxyl terminal amino acid, and addition of palmitate, as shown in Fig. 9. Especially, farnesylation is considered to be essential for translocation of Ras to the cell membrane and Ras functions. Farnesylation of Ras is catalyzed by farnesyl transferase with farnesyl pyrophosphate, which is derived from mevalonate. Mevalonate is synthesized by HMG-CoA reductase, a rate-limiting enzyme of the mevalonate pathway. Therefore, inhibition of this enzyme will reduce farnesylation of Ras. 

Judging from the number of carbon atoms (15) and the pattern of their methyl groups, these closely related compounds are clearly sequiterpenes. They can both be derived from the same intermediate by cyclization of farnesyl pyrophosphate without the need to isomerize an alkene. The eleven-membered ring in humulene can accommodate three E-alkenes. 

Fig. 2. A section of the isoprenoid pathway illustrating the branch to rubber biosynthesis. Rubber (the product) is synthesized in the cytosol from one molecule of allylic pyrophosphate (the initiator) and many molecules of isopentenyl pyrophosphate (the monomer). Isopentenyl pyrophosphate is produced by the cytosolic mevalonate pathway and by the plastidic methyl-erythritol pathway, as indicated by the shaded boxes. GPP, geranyl pyrophosphate FPP, farnesyl pyrophosphate GGPP, geranylgeranyl pyrophosphate.

The cysteine side chain of CaaX is the nucleophile that reacts with farnesyl pyrophosphate or geranylgeranyl pyrophosphate, forming a thioether and eliminating pyrophosphate. Once the protein has been prenylated, the C—aaX amide bond is hydrolyzed, causing cysteine to become the C-terminal amino acid. Cysteine s carboxyl group is then esterified with a methyl group. 

The results obtained from the incorporation of [2- " C]mevalonate into diacetoxyscirpenol (13) (Dawkins, 1966) were in accord with the double 1,2-methyl shift, proposed by Fishman et al (1959) and Jones and Lowe (1960). A similar kind of migration was also observed in the course of investigations on the biosynthesis of verrucarol (49) (Kocor and Siewinski, 1966). A y-bisabolene derivative such as 58 (see Fig. 10) was postulated to be a key intermediate in the biosynthesis of the trichothecenes (Godtfredsen and Vangedal, 1965 Parker et al, 1961 Ruzicka, 1963 Sigg et al, 1965). Hanson and Achilladelis (1967) and Achilladelis and Hanson (1968) demonstrated that farnesyl pyrophosphate acts as a precursor of the trichothecenes. 

These results provide further support for the suggestion that 6J-trans-farnesyl pyrophosphate (56) acts as an intermediate in the biosynthesis of the trichothecene skeleton. That the two methyl groups of the starter prenyl unit of this farnesyl pyrophosphate retain their individuality during the subsequent biosynthetic transformations was shown by Jones and Lowe (1960)... 

Previous C-labelling studies had indicated that andibenin B (110) was formed by a novel pathway in which a bis-C-methylated tetraketide-derived phenolic precursor is alkylated by farnesyl pyrophosphate to give (109) followed by cyclisation, intramolecular cycloaddition, and oxidative modification. Further... 

---