Presented by Gurudutt Dubey 1
• Introduction
• Useful Bases in Peptide Synthesis
• Coupling Agents
1. Carbodiimide reagents
2. Racemization suppressants
3. Phosphonium reagents
4. Aminium/Uronium-Immonium reagents
5. Imidazolium reagents
6. Organophosphorous reagents
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• Application of DCC in solid-phase synthesis is limited due to the by-product dicyclohexylurea (DCU)
with is formed simultaneously with the coupling reaction
• DIC is a useful reagent for automated SPPS, because the corresponding urea is soluble in standard
solvents such as isopropanol and can be washed out readily
If base-free conditions are required as to minimize racemization, the combination of DIC and HOBt
(or HOAt, Oxyma Pure) is still one of the best methods e.g. for coupling Fmoc-Cys(Trt)-OH.
• EDC has also been employed in SPPS on highly polar resins compatible with water-containing
solvents. Contrary to DCU, the urea formed from EDC is readily soluble.
In addition to racemization another side reaction with carbodiimides is an O-N migration of
the activated carboxyl function forming an N-acyl urea
• low temperatures are always recommended
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Oxyma Pure®
(Ethyl 2-cyano-2-
(hydroximino)acetate)
HOAt
(1-Hydroxy-7-aza-1H-benzotriazole)
HOSu
(N-Hydroxysuccinimide)
HOOBt (HODhbt)
(Hydroxy-3,4-dihydro-4-oxo-1,2,3-
benzotriazine)
HOBt
(1-Hydroxybenzotriazole)
HOBt-6-sulfonamidomethyl resin · HCl
(200-400 mesh)
(1-Hydroxybenzotriazole-6-
sulfonamidomethyl resin · HCl)
2. Racemization Suppressants
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3. Phosphonium Reagents
BOP (Q-1980)(Benzotriazol-1-yloxy-tris(dimethylamino)-
phosphonium hexaflorophosphate)
PyBOP® (Q-2715)(Benzotriazol-1-yloxy-tripyrrolidino-phosphonium hexaflorophosphate)
PyAOP(7-Aza-benzotriazol-1-yloxy-
tripyrrolidinophosphonium hexaflorophosphate)
PyOxim (Q-2760)(Ethyl cyano(hydroxyimino)acetato-O2)-
tri-(1-pyrrolidinyl)-phosphonium hexaflorophosphate)
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4. Aminium/Uronium-Imonium Reagents
TBTU (BF4-) (Q-1665)/ HBTU (PF6
-)(2-(1H-Benzotriazol-1-yl)-N,N,N’,N’-
tetramethylaminium tetrafloroborate/ hexaflorophosphate)
HCTU(2-(6-Chloro-1H-benzotriazol-1-yl)-
N,N,N’,N’-tetramethylaminiumhexaflorophosphate)
HDMC (Q-2765)(N-[(5-Chloro-1H-benzotriazol-1-yl)-
dimethylamino-morpholino]-uranium hexaflorophosphate N-oxide)
COMU (Q-2735)(1-[1-(Cyano-2-ethoxy-2-
oxoethylideneaminooxy)-dimethylamino-morpholino]-uronium hexaflorophosphate)
TATU (BF4-) (Q-2150)/ HATU (PF6
-) (Q-2780)(2-(7-Aza-1H-benzotriazol-1-yl)-N,N,N’,N’-
tetramethylaminiumtetrafloroborate/hexaflorophosphate)
TOTT (Q-2600)(2-(1-Oxy-pyridin-2-yl)-1,1,3,3-
tetramethylisothiouronium tetrafloroborate)
TFFH (Q-2280)(Tetramethylfloroformamidinium hexaflorophosphate)
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5. Imidazolium Reagents
CBMIT1,1′-Carbonylbis(3-
methylimidazolium) triflate
CDI (N,N'-Carbonyldiimidazole)
CIP/CIB2-Chloro-1,3-dimethylimidazolinium
hexafluorophosphate/tetrafluoroborate
BOI2-(1H-Benzotriazol-1-yloxy)-1,3-dimethylimidazolidium
Hexafluorophosphate
CMBI2-chloro-1,3-dimethyl-1H-benzo[d]imidazol-3-ium
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DPPADiphenylphosphoryl azide
MPTADimethylphosphinothioylazide
DPP-ClDiphenylphosphinic chloride
BOP-ClBis(2-oxo-3-oxazolidinyl)phosphinic
chloride
MPTO3-Dimethylphosphinothioyl-
2(3H)-oxazolone
FDPPPentafluorophenyl
diphenylphosphinate
6. Organophosphorous Reagents
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References
1. So-Yeop Han, S. Y.; Kim, Y. A. Tetrahedron 2004, 60, 2447–2467.
2. Valeur, E.; Bradley, M. Chem. Soc. Rev. 2009, 38, 606-631.