TFA-peptides

Analytical Cl8 reversed-phase HPLC was performed. Buffer A contained 5% acetonitrile in 0.045% TFA. Buffer B contained 60% acetonitrile in 0.037% TFA. Peptides were eluted with a 10-40% buffer B linear gradient over 30 min at 1.5 ml/min, monitored at 220 nm. 

Observations - Stable against 1 % TFA. - Peptide synthesis with Ppoc-N-protection. ... 

In 1952, F. Weygand started his studies with trifluoroacetic acid (TFA) in peptide chemistry. TFA-amino acids and TFA-peptides showed themselves to lose the TFA residue by treatment with dilute aqueous hydroxides or with piperidine. The volatility of TFA esters allowing the separation of amino acids and peptides by gas chromatography was mentioned on page 54. 

Concentrate the TFA-peptide mixture by nitrogen flow to approx. I mL. 

Filtrate the resin and collect the TFA-peptide mixture. Wash the resin with TFA and DCM and collect the filtrates. 

Cycloalkyl esters have.been used to protect the /3-CO2H group in aspartyl peptides to minimize aspartimide formation during acidic or basic reactions. Aspartimide foimation is limited to 2-3% in TFA (20 h, 25°), 5-7% with HF at 0°, and 1.5-4% TfOH (thioanisole in TFA). Cycloalkyl esters are also stable to Et3N, whereas use of the benzyl ester leads to 25 % aspartimide formation during Et3N treatment. Cycloalkyl esters are stable to CF3COOH, but are readily cleaved with HF or TfOH. - ... 

Tri.-nethylsilyl triflate (TMSOTf), PhSCH, CF3COOH. These conditions also cleave the following protective groups used in peptide synthesis (MeO)Z-, Bn-, Ts-, CI2C6H3CH2-, BOM (benzyloxymethyl)-, Mts-, MBS-, r-Bu-SR, Ad-SR, but not a BnSR, Acm, or Arg(N02) group. The rate of cleavage is reported to be faster than with TfOH/TFA. 

Amphoteric hydrophobic Blue dextran, collagen, gelatin, hydrophobic proteins Hydrophobic peptides Buffer or salt solution with organic solvent (e,g, 20% CH3CN in 0.1 M NaNOi) 35-45% CH3CN in 0.1% TFA... 

FIGURE 5.19 N-Tertninal analysis using Edman s reagent, phenylisothiocyanate. Phenylisothiocyanate combines with the N-terminus of a peptide under mildly alkaline conditions to form a phenylthiocarbamoyl substitution. Upon treatment with TFA (trifluo-roacetic acid), this cyclizes to release the N-terminal amino acid residue as a thiazolinone derivative, but the other peptide bonds are not hydrolyzed. Organic extraction and treatment with aqueous acid yield the N-terminal amino acid as a phenylthiohydantoin (PTH) derivative. 

Cleavage is effected with acid. The following table compares the acidolysis rates with Bn and cyclohexyl esters in TFA/phenol at 43°. The Dmp group reduces aspartimide formation during Fmoc-based peptide synthesis. 

The Phacm group is stable to the following conditions DIEA-CH2CI2, TFA-CH2CI2, piperidine-DMF, 0.1 M TBAF-DMF, and DBU-DMF for 24 h at It to HF-anisole or / -cresol (9 1) at 0° for 1 h and to TFA-scavengers (phenol, HSCH2CH2SH, p-cresol, anisole) for 2 h at 25°. It is partially stable (>80%) to TFMSA-TFA-/ -cresol for 2 h at 25°. These stability characteristics make the group compatible with BOC- or Fmoc-based peptide synthesis. ... 

TsOH, THF, CH2CI2, 5 min. This method was developed for solid-phase peptide synthesis as a safe large-scale alternative to the use of TFA, which is expensive, corrosive, and a waste problem on a large scale." ... 

Me3SiCl, PhOH, CH2CI2, 20 min, 100% yield." Under these conditions, benzyl groups are not cleaved and thus provide marked improvement over the conventional 50% TFA/CH2CI2 used in peptide synthesis. 

The dimethoxybenzyl group was used for backbone protection of the pseudopeptides of the form Xaai/r(CH2N)Gly (Xaa = amino acid). It is introduced by reductive alkylation with the aldehyde and NaCNBH3. Acidolysis with TFMSA in TFA/thioanisole is used to remove it from the amine, but the efficiency is dependent upon the peptide sequence. ... 

The Doc group, introduced with the chloroformate and either DMAP or /-BuOK, is quite acid stable, but can be cleaved with TFMSA-thioanisole-EDT-TFA (10 min, rt) or with / -cresol-HF (1 h, 0°). The Doc group was found to be suitable for tryptophan protection in /-Bu-based peptide synthesis, since no /-butylation of tryptophan was observed during acid deprotection. 

This group is used for peptide backbone protection. The acetoxy group makes it stable to TFA that is used to cleave the BOC group during peptide synthesis. 

When the Ac group is removed (20% piperidine/DMF or 5% hydrazine/DMF), it becomes the Hmb group that is used to improve solubility and prevent aspar-tamide formation and is readily cleaved with TFA. The related 2-Fmoc-4-methoxybenzyl group has also been prepared and used in peptide synthesis. ... 

These derivatives provide effective protection for phosphotyrosine in Fmoc-based peptide synthesis. They are cleaved with 95% TFA. ... 

Fig. 3-2. Semipreparative RP-HPLC profile of eyelo(Arg-Lys-X-Pro-X-Ala). The erude sublibrary (160 mol) was dissolved in 0.1 % (v/v) TFA and applied to a Whatman Partisil 10 pm ODS-2 (1 x 50 em) eolumn. The peaks were eluted using a 40-min linear gradient of 0-25 % aeetonitrile in water at a flowrate of 7 mL min . Fractions were collected every 2 min and pooled in three fractions as indicated by arrows 130 pmol of peptides was reeovered (yield 81 %). (Reprinted with permission from ref. [75]. Copyright 1998, Ameriean Chemieal Soeiety.)...

The macrocyclization of a peptide was carried out by nucleophihc substitution on a fluorobenzene by the sulfide group of the terminal cysteine of a pentapeptide [164]. The peptide 261 was prepared by standard SPPS and was cyclized under microwave irradiation at 50 °C for 10 min in DMF (Scheme 96). The yields of 262, after cleavage with TFA, were remarkably high for a macrocyclic peptide (70%) and also the resulting HPLC purity was very high. 

HPLC High Performance Liquid Chromatography LHRH Lutenizing Hormone Releasing Hormone PTC Phase transfer catalyst SPPS Solid Phase Peptide Synthesis TFA Trifluoro acetic acid... 

The first version of SPPS to be developed used the t-Boc group as the amino-protecting group. f-Boc can be cleaved with relatively mild acidic treatment and TFA is usually used. The original coupling reagents utilized for SPPS were carbodiimides. In addition to dicyclohexylcarbodiimide (DCCI), N, (V -diisopropylcarbodiimide (DIPCDI) is often used. The mechanism of peptide coupling by carbodiimides was... 

Figure 6 High-speed tryptic fingerprint. Horse cytochrome c was digested with trypsin and the peptide chromatographed in acetonitrile water 0.1% TFA at various temperatures and flow rates on a 15 x 0.2-cm PS-DVB column packed with 3-p, 300-A particles, (a) 26°C and 0.5 ml/min. (b) 42°C and 0.7 ml/min. (c) 70°C and 1.1 ml/min. Detection at 220 nm. Note that the resolution rises with the speed of separation.89 (From Swadesh, ]., BioTechniques, 9, 626, 1990. With permission.)...

In an extension to the xanthenyl theme, the benzyl hydrogen was replaced with a substituted / -methoxyphenyl ring to give linker 35 (Scheme 10) [41]. Peptide amides were cleaved rapidly and in high purity with TFA-DCM (1 9) for 15 min or as a protected fragment with TFA-DCM (1 99) for 3-10 min. 

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