Thioesters are compounds resulting from the bonding of
sulfurwith an acylgroup with the general formula R-S-CO-R'. They are the product of esterificationbetween a carboxylic acidand a thiol(as opposed to an alcoholin regular esters).
biochemistrya thioester connects the acetyl groups in acetyl-CoAand malonyl-CoA.
Thioesters and the origin of life
Some biochemists believe that the thioester bond was critical for the
origin of life. One Nobel Prizewinning scientist, Belgium's Christian de Duve, posits a "Thioester World," which preceded and developed into an " RNA World," itself the immediate precursor to the appearance of entities we would call organisms. [de Duve, Christian (Sept./Oct. 1995), "American Scientist"]
As de Duve explains:
:"A thioester forms when a
sulfhydryl(whose general form is written as an organic group, R, bonded with sulfur and hydrogen, hence R-SH) joins with a carboxylic acid(R'-COOH). A molecule of water(H2O) is released in the process, and what remains is a thioester: R-S-CO-R'. ..."
:"It is revealing that thioesters are obligatory intermediates in several key processes in which ATP is either used or regenerated. Thioesters are involved in the synthesis of all
esters, including those found in complex lipids. They also participate in the synthesis of a number of other cellular components, including peptides, fatty acids, sterols, terpenes, porphyrins, and others. In addition, thioesters are formed as key intermediates in several particularly ancient processes that result in the assembly of ATP. In both these instances, the thioester is closer than ATP to the process that uses or yields energy. In other words, thioesters could have actually played the role of ATP in a thioester world initially devoid of ATP. Eventually, [these] thioesters could have served to usher in ATP through its ability to support the formation of bonds between phosphate groups."
Thionoesters are isomeric with thioesters. In a thionoester, sulfur replaces the carbonyl oxygen in an
ester. Methyl thionobenzoate is C6H5C(S)OCH3. Such compounds are typically prepared by the reaction of the thioacyl chloride with an alcohol, but they can also be made by the reaction of Lawesson's reagentwith esters. [R. J. Cremlyn “An Introduction to Organosulfur Chemistry” John Wiley and Sons: Chichester (1996). ISBN 0 471 95512 4.]
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