Stilbenes synthesis

The peanut chalcone synthase and parsley stilbene synthases have been cloned, expressed in E. colt, and purified to homogeneity [135,137]. The enzymes appear to be mechanistically similar each catalyzes the formation of a tetraketide from three molecules of malonyl CoA that are decarboxylated and condensed with a starter unit derived from p-coumaroyl CoA or a similar CoA thioester (Fig. 6). No reductions or dehydrations occur during either chalcone or stilbene synthesis, and some products spontaneously cyclize following their release from the enzyme. A major feature that distinguishes chalcone and stilbene synthases is that the latter perform an additional decarboxylation to remove a carbon atom that is present in chalcone products [132,138]. The presence of this additional carboxyl group results in a different cyclization pattern for chalcone products. The precise mechanisms by which chalcone and stilbene synthases determine the fate of this carbon atom are not known. 

SHAFIPLESS Asymmetne epoxidation 343 SHARPLESS Asymmetric d tydroxylalion 344 SHERAOSKY Rearrangement 345 SHESTAKOV Hydrazine synthesis 346 SIEGRIST Stilbene synthesis 347 SIMMONS - SMITH Cydopropane synthesis 348... 

Stilbenes synthesis by Heck coupling, 43 Stille coupling aryl triflate + organylstannane, 42 Stobbe condensation, 58-59 Stork reagent, 328-329 Strain, steric. See Steric strain Strecker s synthesis of a-amino acids, 50, 301 L-Streptose synthesis, 267 Styrene. See Benzene, ethenyl-Succinic acid. See Butanedioic acid Succinimide. See 2,5-Pyrrolidinedione Sugars. See Monosaccharides Oligosaccharides inexpensive derivs. pr. (table), 263-264 Sulfafurazole, 307 Sulfamethoxazole, 308 Sulfenic acids, esters ... 

Reactions of Methylenephosphoranes - Aldehydes.—The use of the Wittig and Horner reactions in stilbene synthesis has been reviewed. ... 

A method of stilbene synthesis via homocoupling of aryl aldehyde tosyDiydrazones in the presence of lithium fert-butoxide and trimethyl borate under reflux in THF has been described. 

SCHEME 16.21 Stilbene synthesis via Diels-AlderAVittig/oxidation sequence. 

The second-generation Hoveyda catalyst 4 showed good solubility in RTILs with concomitant lower leaching. It was used to test the influence of the [bmim] counteranion and the alkyl group on the imidazolium cation. Contrary to the results reported by Tang on stilbene synthesis, the BFC anion provided here the best result in terms of activity, 92% conversion vs 80% for PFg, and 47% for NTf2 . In all three cases the selectivity toward 7-tetradecene was... 

Scheme 5-45. Fujiwara-Moritani reaction with a styrene to yield a stilbene Synthesis of pterostilbene.

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