HCTU is an aminium coupling reagent used in

peptide synthesis In organic chemistry, peptide synthesis is the production of peptides, compounds where multiple amino acids are linked via amide bonds, also known as peptide bonds. Peptides are chemically synthesized by the condensation reaction of the carboxyl ...

. It is analogous to

HBTU HBTU (2-(1''H''-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate, Hexafluorophosphate Benzotriazole Tetramethyl Uronium) is a Coupling reaction, coupling reagent used in solid phase peptide synthesis. It was introduced in 1978 and ...

. The HOBt moiety has a chlorine in the 6 position which improves reaction rates and the synthesis of difficult couplings

References

Peptide coupling reagents Hexafluorophosphates {{organic-compound-stub