1-Hydroxybenzotriazole, solid phase

Another solid phase fragment condensation with CDI and 1-hydroxybenzotriazole in the synthesis of the human insulin B-chain afforded the oligopeptide in 75% yield. The reaction time with the coupling pair CDI/HOBt was shorter than in the case of the DCC/ HOBt system.136 The CDI/HOBt activation method was also applied to the synthesis of a... 

The earliest published example of microwave-assisted SPOS involved diisopropyl-carbodiimide (DlC)-mediated solid-phase peptide couplings [24], Numerous Fmoc-protected amino acids and peptide fragments were coupled with glycine-preloaded polystyrene Wang resin (PS-Wang) in DMF, using either the symmetric anhydride or preformed N-hydroxybenzotriazole active esters (HOBt) as precursors (Scheme 12.1). 

Using the automated stepwise method of synthesis on a solid phase allows the synthesis of polypeptides consisting of up to 120 amino acids. The final polypeptide is purified by HLPC (high pressure liquid chromatography). O-glycopeptides are also constructed on a solid phase using DCC and N-hydroxybenzotriazole in DMF. ... 

Transport peptides can be synthesized using either t-Boc or Fmoc solid phase peptide synthesis strategies with a synthesizer or manually. We routinely synthesize CPPs in a stepwise manner on solid support using an Applied Biosystems Model 431A peptide synthesizer. tert-Butyloxycarbonyl amino acids are coupled as 1-hydroxybenzotriazole (HOBt) esters to a p-methylbenzylhydryl-amine (MBHA) resin (65). C-terminally amidated CPPs are less prone to degradation and show higher internalization efficiency than carboxylic acid derivatives. 

The ferrocenoyl 1-hydroxybenzotriazole ester 66 reacts with aminoferrocene to give difer-rocenyl diamide 68 (Scheme 12.16).54 Heinze was able to make use of this flexible building block and used it to incorporate it into a peptide backbone by solid-phase synthesis.90... 

Different coupling conditions have been employed to incorporate protected glycosylated amino acids on the solid phase. Carbodiimides (e.g., DCC Fig. 6, 16) with 1-hydroxybenzotriazole (HOBt) (Fig. 6, 17) used as an auxiliary agent have been extensively employed for in situ activation of protected glycosylated amino acids in solid-phase synthesis [24-27,32,34,49,63,67]. Other coupling agents such as BOP (Fig. 6,18) [51,] BOP-HOBt (1 1) [31], TBTU (Fig. 6, 19) [17,28,54] (Fig. 6, 20) [23], PyBOP (Fig. 6, 21) [53], and PfPyU (Fig. 6, 22) [19] in the presence of A -A -diisopropylethylamine or A/ -methylmorpholine have also been used to activate the carboxyl function of protected glycoamino acids. 

Goff and Zuckermann [51] reported the synthesis of 2-oxopiperazine 16 by intramolecular Michael addition on the solid phase. The coupling of resin-bound unsaturated dipeptoids with a variety of Fmoc-L-amino acids, N,N -diisopropylcarbodiimide (DIPCDI), and 1-hydroxybenzotriazole (HOBt) affords tripeptoids, which after treatment with 20% piperidine in DMF, were acylated with benzoyl chloride-EtaN in 1,2-dichloroethane. Following treatment with 95% TFA in H2O, a diastereomeric ratio of monoketopiperazines 16 was obtained (Fig. 8). Rather than benzoyl chloride, phenylisocyanate or bromoacetic acid and an amine could be used. 

Figure 2.2 Modern solid phase peptide synthesis. Process begins with a-N terminal Fmoc deprotection of resin bound C-terminal amino acid residue with piperidine (mechanism illustrated). Peptide link formation follows (typical solvent Al-methylpyrrolidone [NMP]) by carboxyl group activation with dicyclohexylcarbodiimide (DCC) (mechanism illustrated) in presence of hydroxybenzotriazole (HOBt). HOBt probably replaces DCC as an activated leaving group helping to reduce a-racemization during peptide link formation. Other effective coupling agents used in place of DCC/HOBt are HBTU 2-(lH-benzotriazol-l-yl)-l,l,3,3-tetramethyluronium hexafluorophosphate Py-BOP benzotriazole-l-yl-oxy-tns-pyrrolidino-phosphonium hexafluorophosphate. The Process of a-N deprotection, and peptide link formation, continues for as many times as required (n-times), prior to global deprotection and resin removal.

Peptide synthesis. Coupling reactions in peptide synthesis using active esters are greatly accelerated in the solution phase or the solid phase by addition of 1-hydroxybenzotriazole. 

The synthesis of glycopeptides of L-asparagine by the solid-phase procedure required a derivative protected, for example, by the acid-labile N-(ferf-butoxycarbonyl) group. Thus, 1-benzyl N-(terf-butoxycarbonyl)-L-aspartate (88) was condensed with 2,3,4,6-tetra-0-acetyl-)3-D-gluco-pyranosylamine (2), or the 2-acetamido-2-deoxy analog 8, by the active ester method in the presence of DCC and 1-hydroxybenzotriazole, to give 89 and 90, respectively ... 

Solid-phase synthesis was initiated by coupling 5-(4-formyl-3,5-dimethoxyphenyloxy)valeric acid (PAL linker, 0 cf. Chapter 1.7) to amine derivatised crowns using diisopropylcarbodiimide hydroxybenzotriazole in DMF to give 79. Subsequent reductive alkylation of 78 by means of triacetoxyborohydride in DMF containing 1% of AcOH led to the desired central template linked to the solid support 80 as depicted in Scheme 4.1.16. 

The application of additives was investigated in order to suppress or diminish side reactions (A-acyl urea formation and racemization). Al-Hydroxysuccinimide (HOSu), 1-hydroxybenzotriazole (HoBt), and ethyl l-hydroxy-lH-l,2,3-triazole-4-carboxylate are potential additives in the DCC-based coupling synthesis. Solid-phase peptide synthesis (SPPS) is a variant of the linear (stepwise) coupling of amino acids in the C N direction using two major protection groups Boc/Bzl (iert-butoxycarbonyl/benzyl) and Fmoc/tBu (/9-fluorenylmethoxycarbonyl/ieri-butyl). The synthetic scheme for peptides on a polymer (Atherton and Sheppard, 1989 Fields, 1997) is illustrated in Figure 8.1. 

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