Thiol acids conversion

Final purification by use of metal complexes was also applied in the syntheses of the ligands XS4—H4. These ligands exclusively contain thiolate donors and were prepared by Hahn et al. (23) using 2,3-dimercaptobenzoic acid as starting material (Scheme 8). Isopropyl or benzyl protection of the thiol functions, conversion into the acyl chlorides, reaction with a,oo-diamines, and deprotection of the sulfur atoms enabled the connection of two 1,2-benzene-dithiol units via carboxylic acid amide bonds. 

Thiol esters have recently found broad applications in organic synthesis. Two methods for their preparation from acid chlorides and acids are described in the preparation of 2-METHYLPROPANE-2-THIOL ESTERS OF CYCLOHEXANECARBOXYLIC ACID AND CHOLIC ACID. Conversion of the former thiol ester to the corresponding O-t-butyl ester illustrates a general method for the preparation of O-ESTERS FROM THE CORRESPONDING THIOL ESTERS. 

The actual preparation of the tetrapeptide amide required several steps, among them acylation with di-benzyloxycarbonyl-L-cystine, activated in the form of acid chloride, removal of the benzyloxycarbonyl group by reduction with sodium in liquid ammonia, rebenzylation of the thiol group, conversion to benzyl ester and then to the amide. The tetrapeptide amide was secured in crystalline form. 

General Reaction Chemistry of Sulfonic Acids. Sulfonic acids may be used to produce sulfonic acid esters, which are derived from epoxides, olefins, alkynes, aHenes, and ketenes, as shown in Figure 1 (10). Sulfonic acids may be converted to sulfonamides via reaction with an amine in the presence of phosphoms oxychloride [10025-87-3] POCl (H)- Because sulfonic acids are generally not converted directiy to sulfonamides, the reaction most likely involves a sulfonyl chloride intermediate. Phosphoms pentachlotide [10026-13-8] and phosphoms pentabromide [7789-69-7] can be used to convert sulfonic acids to the corresponding sulfonyl haUdes (12,13). The conversion may also be accompHshed by continuous electrolysis of thiols or disulfides in the presence of aqueous HCl [7647-01-0] (14) or by direct sulfonation with chlorosulfuric acid. Sulfonyl fluorides are typically prepared by direct sulfonation with fluorosulfutic acid [7789-21-17, or by reaction of the sulfonic acid or sulfonate with fluorosulfutic acid. Halogenation of sulfonic acids, which avoids production of a sulfonyl haUde, can be achieved under oxidative halogenation conditions (15). 

Nitrogen nucleophiles used to diplace the 3 -acetoxy group include substituted pyridines, quinolines, pyrimidines, triazoles, pyrazoles, azide, and even aniline and methylaniline if the pH is controlled at 7.5. Sulfur nucleophiles include aLkylthiols, thiosulfate, thio and dithio acids, carbamates and carbonates, thioureas, thioamides, and most importandy, from a biological viewpoint, heterocycHc thiols. The yields of the displacement reactions vary widely. Two general approaches for improving 3 -acetoxy displacement have been reported. One approach involves initial, or in situ conversion of the acetoxy moiety to a more facile leaving group. The other approach utilizes Lewis or Brmnsted acid activation (87). 

The succinimide derivative (234) can be used in peptide synthesis for conversion of amino acids into their succinimide esters (235 Scheme 41) (79CL1265). 3-Substituted mercapto-1,2-benzisothiazole 1,1-dioxides (236) have been recommended as an odourless means of storage of thiols. The latter are readily regenerated by the action of piperidine (81CL1457). 

Caiboo-oxygen bonds can be made using the synthetically uninteresting conversion of RMgX into ROH (shown as the firat reacdoo listed above) direct acid hydrolysis of the petxuto compound ROOMgX yields the hydroperoxide ROOM. Caibon-sulfiir bonds can be constructed using Ss to make thiols or thioethers, and similar reacdons are known for Se and Te ... 

Tiazofurine (142) is an antimetabolite with antineoplastic activity. It preferentially affects leukemic lymphocytes over normal cells due to selective activation by formation of its adenine dinucleotide by transformed cells. Of the syntheses available, one starts by conversion of iniidate 138 to methyl 2,5-anhydroallonothioate (139). Next, condensation with ethyl 2-amino-2-cyanoac-etate leads to the thioamide which undergoes thiol addition to the nitrile function to produce the amminothiazolecarboxyester system of 140 directly. Sodium nitrite in aqueous hypophosphorus acid eliminates the superfluous amino group via the diazonium transformation to give 141. This synthesis of tiazofurine (142) concludes by ester amide exchange in methanolic ammonia [48]. 

Ring contractions of pyran derivatives are occasionally valuable. The contraction of 3-halo-2-pyrones to 2-furoic acids under the influence of alkali has been studied and the conditions defined.58112113 The method is adaptable to the preparation of 3-furoic acid via furan-2,4-dicarboxylic acid58 and of 3,4,5-triphenylfuran-2-carboxylic acid.113 Another ring contraction involving halides is the conversion of 4-chloromethylpyrylium salts into furylmethyl ketones as indicated in Scheme 21.114 Pyridine oxides may be transformed with unexpected ease into furans through treatment with a thiol (Scheme 22).115... 

Mopper [265] has described developments in the reverse phase performance liquid chromatographic determination of amino acids in seawater. He describes the development of a simple, highly sensitive procedure based on the conversion of dissolved free amino acids to highly fluorescent, moderately hydrophobic isoindoles by a derivatisation reaction with excess o-phthalaldehyde and a thiol, directly in seawater. Reacted seawater samples were injected without further treatment into a reverse-phase high-performance liquid chromato-... 

Compounds with an acidity constant, pK, in the range of 4 to 10, i.e. weak organic acids or bases, are present in two species forms at ambient pH. This pA a.i. range includes aromatic alcohols and thiols, carboxylic acids, aromatic amines and heterocyclic amines [15]. Conversely, alkyl-H and saturated alcohols do not undergo protonation/deprotonation in water (pA iw 14). 

Hi) Synthesis of S-prenylated peptides Various syntheses of S-prenylated peptides " have relied on the assembly of the peptide backbone on the solid phase, using standard protocols, and subsequent S-prenylation in solution. As a consequence, any final deprotection steps of other amino acids after the S-prenylation cannot be performed under strongly acidic conditions due to the acid lability of the prenyl group. The prenylation reactions themselves can he carried out under basic or mildly acidic conditions. Typical synthesis problems that arise during the S-alkylation are (1) incomplete conversion because of solubility problems, (2) oxidation of the thiol group to disulfides under basic conditions, (3) formation of the sulfonium... 

This enzyme [EC 3.4.19.3], a member of the C15 peptidase family, is also known as pyroglutamyl-peptidase 1,5-oxoprolyl-peptidase, pyrrolidone-carboxylate peptidase, and pyroglutamyl aminopeptidase. This hydrolase catalyzes the conversion of a 5-oxoprolyl-peptide to produce 5-oxoproline and a peptide. The enzyme will not act on the 5-oxoprolyl peptide if the adjacent amino acid is l-proline. Enzyme activity is inhibited by thiol-blocking reagents. 

When 2,5-diphenylfuran was treated with potassium peroxydisulfate, 4-methylquinoline was obtained in quantitative yield. Peroxydisulfate was also found to be a very efficient reagent for the conversion of thiols to disulfides. Sulfides can be selectively converted into the corresponding sulfoxides in the presence of potassium peroxydisulfate in acetic acid. ... 

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