0-Hydroxy thiol esters

Reduction and dehydration. The ketone carbonyl group in acetoacetyl ACP is next reduced to an alcohol by NADPH (nicotinamide adenine dinucleotide phosphate), a reducing coenzyme closely related to NADH. Subsequent dehydration of the resulting /3-hydroxy thiol ester (E2 reaction) in step 7 yields crotonyl ACP, and the carbon-carbon double bond of crotonyl ACP is further reduced by NADPH in step 8 to yield butyryl ACP. 

Possibly, glyoxylase, which catalyses the conversion of j8-keto aldehydes to -hydroxy thiol esters, acts by an analogous sort of intramolecular hydride transfer. 

Hydroxyquinolines, 503 d-Hydroxyselenides, 28, 29, 86, 549 (3-Hydroxyseienocyanates, 487 N-Hydroxysuocinimide, 290, 425 d-Hydroxy sulfides, 363 13-Hydroxy sulfoxides, 5, 561 (3-Hydroxy suifoximines, 395 -Hydroxy thiol esters, 334... 

The authors studied the further possible extension of this enantioselective reaction to the synthesis of syn-a-methyl-p-hydroxy thiol esters and found that the reaction of PhCHO with enol silyl ether 20 in the presence of stoichiomet-... 

Very little attention has been paid in the past to base-induced Claisen-type condensation reactions of thiol-esters, and related reactions. With LiPr jN at — 78 C, ester enolates are formed from thiol-esters having an a-proton, and jS-hydroxy-thiol-esters are readily formed when ketones are added. ... 

Advances have been achieved in recent years, such as the use of CL reagents as labels to derivatize and sensitively determine analytes containing amine, carboxyl, hydroxy, thiol, and other functional groups and their application in HPLC and CE [35, 36], the synthesis and application of new acridinium esters [37], the development of enhanced CL detection of horseradish peroxidase (HRP) labels [38], the use of immobilization techniques for developing CL-based sensors [39-42], some developments of luminol-based CL in relation to its application to time-resolved or solid-surface analysis [43], and the analytical application of electrogenerated CL (ECL) [44-47], among others. 

Hydroxydec-2-enoic acid 397 was identified in the fodder juice of the Weisel cells (gelee royale) of honey bees. One of the synthesis of 397 starts from suberic acid ethylester 393 222) which was first converted into the hydroxyacid 394 and then into the thiol ester 395. Raney nickel reduction of the latter yields an intermediate aldehyde which, in statu nascendi, reacts with the phosphorane 67 to give 396. Subsequent hydrolysis of396affords the ( )-a,0-unsaturated hydroxy acid 397 222) (Scheme 70). 

Methods available before 1971 for the preparation of thiol esters are briefly summarized in a review article.4 Since then, several newer techniques have been developed, to meet a certain set of criteria required for recent synthetic operations. This development may be summarized as follows. Whenever an acid chloride is available, the reaction of the T1(I) salt of a thiolate of virtually any kind, including alkane-, benzene-, 2-benzothiazoline-, and 2-pyridinethiol, proceeds efficiently and near-quan-titatively. However, if selective thiol ester formation in the presence of hydroxy or other functional groups in the same molecule is required, three main procedures are available. First, reaction of an acid (1), with... 

Two superior, alternative reagents for the Corey method are the disulfides 23 and 24 [19], For example, in the first synthesis [20] of erythronolide B (27), the aglycone of the important antibiotic erythromycin B, cyclization of the hydroxy acid 25 to the 14-membered lactone 26 was effected in 50% yield via the thiol ester of 4-r-butyl-iV-isopropyl-2-mercaptoimidazole by heating in dry toluene under reflux (Scheme 9). 

Carbonyl transposition.1 Tetrafluoroboric acid is the most effective acid for rearrangement of a-hydroxy ketene dithioketals to a,p-unsaturated thiol esters. This rearrangement is particularly useful for rearrangement of the tertiary allylic alcohols formed by addition of organometallic reagents to a-keto ketene dithioketals, which are readily available by reaction of ketone enolates with carbon disulfide followed by alkylation with methyl iodide. 

The hydrolysis of thiol esters is achieved in either acidic or basic media. Alcoholic solutions of hydrogen chloride or potassium hydroxide are the most common reagents. Dithiols, hydroxy mercaptans/ and mercapto ethers, ketones, and acids have been prepared by this method. The corresponding thiol esters are obtained by the addition of thioacetic acid to oxides and olefinic acids or by the action of its potassium salt on halo ketones or sulfonic esters. ... 

Activation by addition of a carboxylic acid to a triple bond occurs with ethyl ethynyl ether,which forms amides via reactive enol esters. The reaction is catalyzed by mercury(II) oxide under almost neutral conditions. Push-pull alkynes exert higher reactivityThe intermediate enol esters (Scheme 4) rearrange and react with the amino function of a second amino acid. Hydroxy, thiol and imidazole functional groups do not have to be protected. The degree of racemization is low, and yields are good in the case of small peptides. 

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