Thiols complexes

Thioesters are more reactive towards nucleophilic substitution than oxygen esters, and are widely employed in natural biochemical processes because of this property. Coenzyme A is a structurally complex thiol, and functions in the transfer of acetyl groups via its thioester acetyl coenzyme A (acetyl-CoA CH3CO-SC0A). 

Nature employs nucleophilic aQ l aubstitntion reactioiLs in the biosynthesis of many molecules, using thiol eaters for the purpose. Acetyl coenzyme A lavotyl C oA> ia a complex thiol ester that i- employed in living sj stcms to acetylate amines and alcoliola. 

The reactions that produce thioesters are essential in energy-harvesting pathways as a means of "activating" acyl groups for subsequent breakdown reactions. The complex thiol coenzyme A is the most important acyl group activator in the cell. The detailed structure of coenzyme A appears in Section 13.9, but it is generally abbreviated CoA—SH to emphasize the importance of the sulfhydryl group. The most common thioester is the acetyl ester, called acetyl coenzynne A (acetyl CoA). 

Both (K) and (5) isomers of thiorphan exhibit a high affinity for enkephalinase. This indicates that the major interactions between the enzyme and the inhibitor complex (thiol group, phenyl ring and the H-bond involving the amide group) are satisfied by the stereochemistry of both isomers. The inversion of the amide bond, as in retrothiorphan, requires a conformation of the inhibitor, such that only the (R) isomer is able to interact satisfactorily to form the enzyme-inhibitor complex, the inhibitory potency of the (5) isomer being reduced nearly a 100-fold. It appears that... 

AuSR C N molar ratios. The spectra for fg—Au—C N and fm—Au—C N were similar. In both cases the N chemical shifts are located at ca 260.30 ppm. Up to a 2 1 ratio of Autm C N the resonance at 265 ppm attributed to Au(CN)2 did not appear. At higher concentrations of C N this resonance has been observed and was increasing in intensity. The similarity of N chemical shifts indicates that electronic environments of CN ligands are similar in both complexes, since the binding site of complex thiols is at a large distance. The following NMR data have been found ... 

So far, the more common ways to use Pummerer chemistry have been described (i.e., 24 26 and 24 25, Scheme 20.7T However, even if it usually is the A fragment fScheme 20.7 of the sulfoxide which is the inportant component of the target, some researchers have used the classical Pummerer reaction to obtain thiols or complex vinyl sulfides (24 28 or 24 27, Scheme 20.7). Clearly, the convenience of using Pummerer chemistry in the synthesis of thiols is closely related to the structure of the desired product. Sinple thiols can be obtained by Pummerer reactions, but in most cases, other shorter and cheaper methods are available. Consequently, the use of the Pummerer rearrangement to produce thiol products is most favorable in the s)mthesis of very complex thiols. 

Aaseth, J, and Friedheim, E.A.H. (1978). Treatment of methyl-mercury poisoning in mice with 2,3-dimercaptosuccinic acid and other complexing thiols. Acta Pharmacol. Toxicol.. 42. 248-252. 

The Hoechst group have developed a synthesis of novel cephem systems which also utilizes a monocyclic azetidine as the starting point for the elaboration of the heterocyclic ring. Displacement of acetate from azetidinone (162) by the complex thiol (163) gave the cepham carbinolamide (164) dehydration produced the cephem (165). > Functionalization at C-7, e.g. (166) -> (168), could be achieved by bromination followed by displacement by azide ion. Using this general approach, compounds (169) and (170) were prepared. ... 

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