3-Selinene synthesis

The PEG precipitate (30- 0%) obtained from the 100,000 g supernatant of the epicarp of immature fruits of calamondin was submitted to chromatography on a column of DEAE-Sephacel and developed with a linear gradient of NaCl (0.1-0.2M). As shown in fig. 1, the limonene and selinene cyclase activities were resolved. The electrophoresis of the fractions involved in mono- and sesquiterpene biosynthesis showed the purification obtained after the DEAE-Sephacel column. Incubations of small gel pieces with [ H]-GPP and [ H]-FPP led to the localization of the cyclases involved in both limonene and selinene synthesis and indicated that the two cyclases are well separated on the gel. In order to improve the purification of these cyclases, the active fractions eluted from the DEAE-Sephacel column were submitted to affinity chromatography using Sepharose APP. This procedure contributed to a 90-fold and 70-fold purification for limonene and selinene cyclases respectively. An isoelectric point of 5A 0.2 was found for limonene-cyclase whereas 3-selinene-cy-clase presented a value of 6 0.2. After gel permeation with Sephadex G 200, the same molecular weight of 67 3 kD was attributed to the two cyclases. In addition, prenyltransferases obtained from a DEAE-Sephacel column developed with a step gradient (0.1, 0.2, 0.3 M NaCl) were also isolated on the same affinity column. These prenyltransferases were 160 fold purified. Their molecular weight was about 70 kD and they exhibited an isoelectric point of 3.2. 

The extrapolation of the vinylcyclopropane-cyclopentene rearrangement to a vinyl-cyclobutaiie-cyclohexene synthesis begins to create new insights into the synthesis of six membered ring natural products. The eudesmane sesquiterpene (—)-P-selinene, 217 illustrates such a strategy as summarized in Scheme 14 80). A suitable cyclohexene... 

The alkoxide generated by KH in THF was believed to be effective in accelerating the vinylcyclobutane ring expansion in the synthesis of 6-membered ring compounds 142). As an example, the cyclobutanol (416) reacted with KH and rearranged to (417), which upon subsequent oxidation, provided (418) 142) in 64.5% yield. The a,P-unsaturated ketone (418) was converted to (—)- 3-selinene (419)142). Similarly, furancyclohexanol (421) could be obtained from the cyclobutanol (420) 142). 

The utility of this stepwise C3 - C4 - C6 ring expansion has been demonstrated by the synthesis of the optically active eudesmane sesquiterpene (—)- 3-selinene 295 starting from the commercially available (—)-perillaldehyde 2871S3). Thus, addition of the 1-lithio-l-methoxycyclopropane 136 (vide supra. Sect. 4.6.3, Eq. (44)) to 287,... 

The protic reaction on occasion is a useful method of alkene formation, but is far from general because the cation intermediate tends to undergo rearrangements.Further, even for cases in which elimination to an alkene is the predominant pathway, the regioselectivity of the process is often mediocre. A key step in the synthesis of (+)-a-eudesmol and (-)-a-selinene exemplifies this point (Scheme 60). There are, however, isolated examples of excellent selectivity, such as the reaction of a 3-ketotetrahydrofuran tosyl-hydrazone salt to give the corresponding cyclic enol ether as the major product (Scheme 61), the intro-... 

Scheme 41. The cation radical Diels-Alder reaction in a formal total synthesis of beta selinene.

The usefulness of the cation radical Diels-Alder reaction for natural product synthesis has been illustrated in the synthesis of / -selinene (Scheme 41) [81], which utilizes phenyl vinyl sulfide as a Diels-Alder dienophile and the photosensitized electron transfer method as the preferable method for generating the corresponding cation radical. 

The protic Bamford-Stevens reaction has been successfully utilized in the asymmetric synthesis of the naturally occurring sesquiterpenes (+)-a-eudesmol and (-)-a-selinene. Here, the more-substituted alkene was formed preferentially (equation 4,1). ... 

Japanese female peach fruit moth have been synthesised (Scheme 10).2 9 The phosphine oxide starting material (51) was obtained from a Wittig reaction of the ylide derived from 1,1-diphenylphospholanium perchlorate. The reaction of (l-methyl-2-propenyl)diphenylphosphine oxide carbanion (55) with the optically active aldehyde (54) is the key step in a short synthesis of the sesquiterpenes (-)-a-selinene (58) and (-t-)-a-helmiscapene... 

Thus, the first step of a stereoselective synthesis of p-selinene reported by Mackenzie, Angelo and Wolinski involves hydroxylation of the C-8-C-9-double bond of (i )-(+)-limonene by hydroboration with diborane and subsequent... 

The four membrane fractions are incubated with [ 1- C] IPP and assayed for 5 enzymic activities. Figure 1 shows that the membranes sedimenting in the upper band A exhibit the greatest activity in the synthesis of sesquiterpene hydrocarbons particularly p-selinene and germacrene D. Lower amounts of radioactivity are also present in B and C whereas only traces of synthesis of hydrocarbons are found in D. 

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