HOAt

A coupling activator for racemization-free coupling in peptide synthesis; An additive for peptide segment coupling in in reducing the extent of configurational loss at the reactive carboxylic acid residue. Carpino L A etc. works demonstrated that the DIC/HOAt system is more effective in preserving configuration for peptide segment coupling than the analogous DIC/HOBt system

in DMF and DCM. [1]

Reference:
Carpino L A, El-Faham A.  The diisopropylcarbodiimide/1-hydroxy-7-azabenzotriazole system: segment coupling and stepwise peptide assembly[J]. Tetrahedron, 1999, 55(22): 6813-6830.

Peptide bond-forming reagents HOAt and HATU are not mutagenic in the bacterial reverse mutation test.[Pubmed:26840011]

Environ Mol Mutagen. 2016 Apr;57(3):236-40.

The peptide bond-forming reagents 1-hydroxy-7-azabenzotriazole (HOAt, CAS 39968-33-7) and O-(7-Azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU, CAS 148893-10-1) either have structural alerts, unclassified features or are considered out of domain when evaluated for potential mutagenicity with in silico programs DEREK and CaseUltra. Since they are commonly used reagents in pharmaceutical drug syntheses, they may become drug substance or drug product impurities and would need to be either controlled to appropriately safe levels or tested for mutagenicity. Both reagents were tested in the bacterial reverse mutation (Ames) test at Covance, under GLP conditions, following the OECD test guideline and ICH S2(R1) recommendations and found to be negative. Our data show that HOAt and HATU-common pharmaceutical synthesis reagents-are not mutagenic, and can be treated as ordinary drug impurities.

Oxyma: an efficient additive for peptide synthesis to replace the benzotriazole-based HOBt and HOAt with a lower risk of explosion.[Pubmed:19575348]

Chemistry. 2009 Sep 21;15(37):9394-403.

Oxyma [ethyl 2-cyano-2-(hydroxyimino)acetate] has been tested as an additive for use in the carbodiimide approach for formation of peptide bonds. Its performance in relation to those of HOBt and HOAt, which have recently been reported to exhibit explosive properties, is reported. Oxyma displayed a remarkable capacity to inhibit racemization, together with impressive coupling efficiency in both automated and manual synthesis, superior to those of HOBt and at least comparable to those of HOAt, and surpassing the latter coupling agent in the more demanding peptide models. Stability assays showed that there was no risk of capping the resin under standard coupling conditions. Finally, calorimetry assays (DSC and ARC) showed decomposition profiles for benzotriazole-based additives that were consistent with their reported explosivities and suggested a lower risk of explosion in the case of Oxyma.

Reactions of monoaryl-substituted methylenecyclobutanes and methylenecyclopropanes with 1-hydroxybenzotriazole (HOBt), 1-hydroxy-7-azabenzotriazole (HOAt), and 1-hydroxysuccinimide (HOSu).[Pubmed:19222218]

J Org Chem. 2009 Mar 20;74(6):2516-20.

Monoaryl-substituted methylenecyclobutanes (MCBs) and methylenecyclopropanes (MCPs) react with 1-hydroxybenzotriazole (HOBt), 1-hydroxy-7-azabenzotriazole (HOAt), and 1-hydroxysuccinimide (HOSu) smoothly to produce the corresponding cyclobutylmethanone and cyclopropylmethanone derivatives 2, 4, and 5 via a cascade epoxidation and nucleophilic addition process or the corresponding epoxides 6 in moderate to good yields under mild conditions. A plausible mechanism has been proposed on the basis of the control experiments and the isolation of the reaction intermediates.