Thionoesters and dithioesters

These compounds are reasonably stable and surprisingly easy to prepare and to handle. Conjugation between the double bond of the thiocarbonyl group and the lone pair on the a heteroatom leads to a good balance between stability and reactivity for these functional groups. 

As mentioned previously, there are reviews which cover the many synthetic methods available [119, 120], and only a few specific aspects of some of the main routes are discussed here for both (3) and (4) the most important method of preparation relies upon the reactivity of imidooesters and imidothioesters towards hydrogen sulfide [135]. 

The thionation of esters and thiolesters by thiophosphorus derivatives and mainly by Lawesson s reagent is another general process (Table 2.2) [136, 137]. 

Synthesis of thionoesters from esters and Lawesson s reagent 

General procedure for the reactions of esters with Lawesson s reagent 

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Extensive studies of enzyme-substrate complexes by resonance Raman spectroscopy (RR) have prompted the synthesis of new peptide bond modifications such as thionoesters and dithioesters (Scheme l7)t82-83l within simple model substrates. The resulting acyl-enzyme complexes are especially amenable to RR analysis with cysteine proteases such as papain due to formation of the transient dithioester intermediates. 

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