Terpenoids synthesis

Terpenoid Synthesis from Isoprene.—Syntheses of the useful synthons (33) and (34) have been reported. The vinyl-oxygen bond of diketen is selectively cleaved by Me3SiCH2MgCl-NiCl2 to yield the synthon (35) which is readily converted into the dicopper dienolate (Vol. 7, p. 14) and prenylated to yield (36 X = C02H) after hydrolytic work-up and desilylation (36 X = C02H) yields... 

Terpenoid Synthesis from Isoprene.—Interest continues in new syntheses of iso-prene and its derivatives the dioxan (37) is obtained108 in good yield by the Prins reaction of methylallyl chloride with formaldehyde (cf. Vol. 5, p. 8) free-radical addition of isopropyl alcohol to vinyl acetate yields compound (38) which gives isoprene by acid-catalysed reaction over alumina.109 (Z)-2-Methylbut-2-en-l-ol and dimethylallyl alcohol are readily available from frans-crotyl alcohol.110... 

As part of a general investigation of terpenoid synthesis from isoprene units it has been shown that condensation of limonene (46) with senecioyl chloride in the presence of stannic chloride, followed by dehydrochlorination, provides a new simple synthetic route to a mixture of cis- (47) and frans-atlantones (48).23a Using acetyl chloride instead of senecioyl chloride in the synthetic sequence provides a C12 trisnor-sesquiterpenoid (49) which co-occurs with trans-atlantone in the essential oil of Cedrus atlantica.23b... 

The prenyltransferases that catalyse the s)mtheses of GPP, FPP and GGPP may be important regulatory enz)mies in plant terpenoid bios)mthesis since they are situated at the primary branch points of the pathway, directing flux among the various major classes of terpenoids. The level of prenyltransferase activity is, in fact, closely correlated with the rate of terpenoid formation in many experimental systems (Dudley et at, 1986 Hanley et at, 1992 Hugueney et at, 1996) consistent with the regulatory importance of these catalysts. The localization of specific prenyltransferases in particular types of tissue or subcellular compartments may control the flux and direction of terpenoid synthesis at these sites. For example, the GPP synthase in Salvia officinalis is restricted to the secretory cells of the glandular trichomes, which are the sole site of monoterpene bios)mthesis in this species (Croteau and Purkett, 1989). 

Methyl-3-propiolactone is useful as a four-carbon building block for terpenoid synthesis (eq 4). Citronellic acid (9) isprepared by reaction with the homoprenyl Grignard reagent pulegone (10), citronellol (11), geraniol, and nerol (12) can be obtained by further functional group manipulations. ... 

Dimethyl-2-cyclopenten-l-one is a valuable starting material in terpenoid synthesis and in cases where a gem-dimethyl cyclopentane unit needs to be introduced. It is useful as a starting material in further functionalization. Its preparation by the method of Magnus is amenable to large scale synthesis. 

Terpenoid Synthesis from Isoprene.—Co-oxidation of thiophenol and isoprene with oxygen yields the synthons (9) and (10) in useful yields and the isoprene epoxide (11) is a useful hemiterpenoid synthon with carbanions. ... 

Excellent reviews have appeared on the synthesis of monoterpenoids,1 of cannabinoids,2 and of the use of isoprene in terpenoid synthesis,3 and also on terpenoids from marine sponges,4 the base-catalysed isomerization of mono-... 

As a standard inhibitor we chose cerulenin, a secondary metabolite of Cephalosporium caeruleus, which is itself fungicidally active and is known to interfere with fatty acid biosynthesis (31 ) as well as HMG-CoA-synthase (32). Mevalonate formation on the level of HMG-CoA-synthase and HMG-CoA-reduction, however, to our knowledge is a relatively poor fungicidal target (33). Nevertheless the potency of cerulenin to interfere with early steps of terpenoid synthesis complicates interpretation. 

The petrochemical building blocks used for terpenoid synthesis are all readily available bulk feedstocks and are therefore free from concerns regarding availability and security of supply, until the supply of mineral oil is exhausted. 

Terpenoid Synthesis from Isoprene.—Some prenylation procedures have been reported earlier. An efficient conversion of prenyl chloride into prenyl acetate has been described and the synthon (31 X = OH) (Vol. 7, p. 10) has... 

Juglone = 5-hydroxy-l,4-naphthalenedione dienophile in tetracycline synthesis, 318 Julia-Lythgoe olefination, 34 Julia s terpenoid synthesis, 69-70 Juvenile hormone synth. steps, 20, 30, 135, 155... 

Acetylenic ketones are useful intermediates in terpenoid synthesis. Coke and co-workers have described a novel synthesis of acetylenic ketones, inspired by, but different from, the Eschenmoser fragmentation. The procedure is illustrated in Scheme 34 by its application to the synthesis of exo-brevicomin (134) the pheromone from Dendroctonus brevicomis. Hydroboration of the double bond of oct-l-en-4-yne with 9-BBN, followed by the acetylene zipper procedure, and base-induced alkyl transfer to t-butyl bromo-methyl ketone offers an efficient route to acetylenic ketones in greater than 70% yield [(135)->(136)]. °... 

Developed in the early 1970s, this reaction, also called the Hajos-Parrish reaction or Hajos-Parrish-Ender-Sauer-Wiechert reaction, is one of the earliest processes for the stereoselective synthesis of Wieland-Miescher ketone, an important building block for steroids and terpenoid synthesis. This reaction is a proline mediated asymmetric variation to the Robinson annulation. Hajos and Parrish of Hoffmann-La Roche Inc. in 1971 and 1974 published an asymmetric aldol cyclization of triketones such as that of structure 39, which affords optically active annulation products in the presence of catalytic amounts of (S)-proline (Z-proline). One of the early examples is the synthesis of 41 from the triketone 39 (a product of the Michael addition of MVK to the corresponding 2-methylcyclopentane-l,3-dione), the reaction is performed in two steps first by ring formation in the presence of 3 mol % of (iS)-proline in DMF to afford the ketol 40 in 100% yield after crystallization with 93% ee and then by reaction with toluenesulfonic acid to give the dehydrated adduct 41. The formation of the Wieland-Miescher Ketone 44 follows the same synthetic route, starting from the tri-ketone 42 to give the end product in 75% optical purity and 99.8% of optical yield. 

Based upon the current knowledge of plant terpenoids reviewed here, we can be reasonably sure that factors related to global climate change will have an impact on terpenoid synthesis in plants and the dispersal of terpenoids in the atmosphere and soil. The ecological functions of terpenoids could be severely disturbed e.g., when atmospheric ozone degrades the important volatile information compounds such as monoterpenes and sesquiterpenes. 

Alvarez-Manzaneda et al. [5] have developed a synthetic strategy toward the tetracyclic marine metabolite puupehenones involving a FC reaction with enone 25, a common enantiopure nordri-mane synthon utilized in terpenoid synthesis, as the electrophilic partner (Scheme 2.4). The reaction is carried out in the presence of the cationic resin Amberlyst A15 to afford ketone 27 in high yield and with complete diastereoselectivity. The reaction only works with highly activated arenes such as 26, as neither anisole nor catechol dimethyl ether reacted under identical conditions. Ketone 27 can be straightforwardly transformed into triflate 30, which is an intermediate in the synthesis of puupehenone-related metabolites such as puupehenol (31). 

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