The concept of superactive esters
- 1 March 1994
- journal article
- Published by Wiley in International Journal of Peptide and Protein Research
- Vol. 43 (3) , 312-319
- https://doi.org/10.1111/j.1399-3011.1994.tb00396.x
Abstract
According to the concept presented, esters forming an amide (peptide) bond by the mechanism S#nDN or S#*NDN involving fast decay of the tetrahedral intermediate may behave as ‘superactive acylating reagents’. These should render coupling involving less reactive substrates, i.e. sterically hindered or ‘difficult coupling sequences’, much faster and more uniform than classic active esters. In extremely cases this advantage could be significant, and the calculated increase in time required for 99.9% coupling substrates 6 pKa units less reactive than the standard ones reaches 2512000 τ1/2 units for classic active esters, but only 631 τ1/2 units for reaction involving ‘superactive esters’. The postulated change of mechanism is expected for esters bearing a leaving group which is able to undergo an additional, synchronous, energetically favored process accompanying its departure, as has been observed in the case of triazine esters. Some advantages of triazine superactive esters in the condensation of sterically hindered substrates are demonstrated.Keywords
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