Elimination, anti conjugate

Recently, elegant synthesis of awft -MRS carbapenum has been reported. Sequential reaction of nitromethane via conjugate addition-elimination to a,P-unsaturated esters followed by Pd-catalyzed substitution of the resulting allyl nitro compound with the naphthosultam affords the allylation product which is an anti (Eq. 7.20).22... 

Selenosulfonylation of olefins in the presence of boron trifluoride etherate produces chiefly or exclusively M products arising from a stereospecific anti addition, from which vinyl sulfones can be obtained by stereospecific oxidation-elimination with m-chloroper-benzoic acid134. When the reaction is carried out on conjugated dienes, with the exception of isoprene, M 1,2-addition products are generally formed selectively from which, through the above-reported oxidation-elimination procedure, 2-(phenylsulfonyl)-l,3-dienes may be prepared (equation 123)135. Interestingly, the selenosulfonylation of butadiene gives quantitatively the 1,4-adduct at room temperature, but selectively 1,2-adducts at 0°C. Furthermore, while the addition to cyclic 1,3-dienes, such as cyclohexadiene and cycloheptadiene, is completely anti stereospecific, the addition to 2,4-hexadienes is nonstereospecific and affords mixtures of erythro and threo isomers. For both (E,E)- and ( ,Z)-2,4-hexadienes, the threo isomer prevails if the reaction is carried out at room temperature. 

The stereochemistry of 338 and 339 in each case results from initial conjugate addition of MeO" at position 2 of the chromone ring. Ensuing attack of the formed enolate 342 upon PhI(OMe)2 occurs in an anti manner because of steric interaction. Sequential addition of MeO to the carbonyl group of 343 gives 344, and intramolecular reductive elimination of C6H5I then occurs with inversion of configuration, 344 345. The reaction is... 

Zhou S, Kestell P, Paxton JW. 2002. Predicting pharmacokinetics and drug interactions in patients from in vitro and in vivo models the experience with 5,6-dimethylxanthenone-4-acetic acid (DMXAA), an anti-cancer drug eliminated mainly by conjugation. Drug Metab Rev 34 751-790. 

Figure 9 shows the curve for tobacco residues purified by TLC before analysis by the assay. It is clear that the interference seen previously was practically eliminated. However, such extensive sample preparation makes use of this assay in its present form cumbersome, at best. We are presently investigating an alternative form of immunoassay, the enzyme immunoassay (EIA) ( , 21) In this assay methoprene is conjugated directly to an enzyme and the anti-methoprene antibody is bound to the solid support. Free methoprene and methoprene-enzyme conjugate are in solution and compete for immobilized antibody binding sites. Unbound methoprene is washed from the assay prior to addition of substrate. Preliminary results under these conditions indicate that tobacco extracts of acetonitrile/water (9 1) do not require further purification steps prior to application to the EIA. 

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