Resins peptide cleavage from

Peptide cleavage from the allyl-linker resin is achieved with morpholine in large excess in the presence of tetrakis(triphenylphosphine)palladium (10mol% based on the allylic substitution of the resin). (3-HYCRAM resin is a modification of HYCRAM containing a P-alanine residue as a spacer between the crotonoyl unit and the resin. It has been used for the solid-phase synthesis of glycopeptides by the Boc and Fmoc strategies.b 1 Difficulties may be... 

In the case of smaller peptides, highly pure products have been obtained in good yields by simple evaporation of filtrate from the resin-peptide cleavage product. If necessary, the product peptide can be purified by ion-exchange chromatography to separate the error-peptides ef-... 

This Fmoc analog is prepared from the chloroformate, O-succinimide, or p-nitrophenyl carbonate and is cleaved with 10% piperidine in 1 1 6M guanidine/IPA. It was designed to interact strongly on a column of porous graphitized carbon so as to aid in the purification of peptides after cleavage from the resin. 

A general procedure for the iodine reaction in the solid phase is shown in Scheme 9. Both Boc and Fmoc chemistry can be used to assemble the linear S-protected bis-cysteine peptides and for thiol protection the well-established Acm and Trt groups are usually used. Suitable solvents for the thiol-deprotection/oxidation step by iodine to form the disulfide are CH2C12, DMF, or aqueous AcOH. The final deblocking and cleavage from the resin is carried out under standard conditions. Modification at sensitive amino acid residues caused... 

Scheme 11 Synthesis of a Lanthionine Peptide via Solid-Phase Peptide Synthesis and Final Cleavage from Kaiser Oxime Resin 481...

The peptide was synthesized on TentaGel S RAM resin (lg, 0.25 mmol loading). Cleavage from the resin and deprotection was performed with TFA/H20/anisole/TIS (88.5 5 5 1.5, 20 mL) for 2 h at rt and the crude product was precipitated with tBuOMe/hexane (2 1) yield of crude product 160 mg. The relatively low yield (28%) is due to reattachment as determined by amino acids analysis of the resin hydrolysate (40% reattachment). The title compound was obtained by preparative HPLC (linear gradient of 0.1% aqTFA/0.08% TFAin MeCN from 90 10 to 40 60 in 105min) yield 40mg (10%) ESI-MS (m/z) Found 2543.2. Calcd for CjcBHisil bjCb Sej 2542.2. 

Postsynthetic intramolecular alkylation of a cysteine thiol group with a bromo amino acid has also been proposed/431 but this approach is limited by the low coupling efficiency of the bromo amino acid in the peptide synthesis due to a competing intramolecular cyclization reaction. A promising new approach consists of using suitably protected cysteine and homoserine derivatives for the peptide synthesis, whereby the side-chain hydroxy group of homoserine is protected as the TBDMS derivative which is converted on resin into the chloro derivative with freshly prepared triphenylphosphine dichloride. Upon cleavage from the resin, cyclization is performed in solution as shown in Scheme 11144]... 

Conversely, exposure to hydrogen fluoride at 0 °C over short periods of time leads to almost quantitative hydrolysis.[37-39] In aprotic organic solvents, decomposition takes place unless the sulfate hemi-ester is neutralized with strong counterions.[37,381 The results of a detailed study are summarized in Figures 1 and 2t4°l which show the effect of various acids used in peptide chemistry in deprotection and in cleavage from the resin as well as the effect of temperature on the hydrolysis of tyrosine 0-sulfate as a sodium salt. 

The crude peptide thioester H-Cys-Ser-Cys-Lys-Ser-Lys-Val-Cys(Acm)-Tyr-Lys-Gln-Ser-Ile-Pro-Cys-Gly-Glu-Ser-Cys-Val-Phe-Ile-Pro-Cys(Acm)-Thr-Val-Thr-Ala-Leu-Leu-Gly-COS(CH2)2CONH2 (50-80mg), obtained after cleavage from the resin support by HF (HF/PhOMe 9 1), was extracted into a 8M urea soln (150 mL) at pH 7.6 in a highly reductive environment containing 5- to 10-fold excess of TCEP and then dialyzed against 8 M urea (2000 mL) to allow cyclization in a descending concentration... 

Cleavage from the Resin The peptide was simultaneously deprotected and cleaved from the resin by a 30-min treatment with neat TFA (sulfur-containing scavengers have to be absent). The resin was filtered and the soln added to cold MTBE. The precipitated peptide was collected and treated with aq NH3 (pH 9.0-9.5) for 3 h at rt in order to restore the chemical integrity of the nitroxide moiety.1 201 HPLC Purification The peptide was purified by RP-HPLC (MeCN/H20 containing 0.1 % TFA). The above-noted NH3 treatment was repeated immediately after the HPLC elution. 

On-resin reduction of the imino bond of the Boc-Tyr[Bzl(2,6-Cl2)]ip[CH=NNH]Leu-peptide-PAM 48 (300mg, 0.204mmol) was carried out for 12h in a DMF/CH2C12 (1 3) by NaBH3CN following the procedure used for the reductive amination to afford 50. 7 The same procedures for deprotection and cleavage from the resin, as described for the iminoaza peptide, were applied. The yield was estimated at about 45%. Fractions determined to be pure by analytical RP-HPLC are pooled, concentrated under reduced pressure and lyophilized to yield the expected reduced iminoaza peptide 51 (white powder >95% pure) which was checked by TOF-MS calcd, 1255.49 [M + l]+ found, 1255.45. 

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