Side-chain deprotection

O-Acylated Hmb is stable to acidolysis by TFA giving a useful additional feature to Hmb-containing peptides. Side-chain protection and the V -protection, if it is first replaced with Boc before Hmb O-acetylation, can be removed and backbone protection retained. After deacetylation of Hmb with aqueous hydrazine the peptide can be further purified before removal of the Hmb groups, useful when the product is poorly soluble. This feature is also useful for the purification of large polypeptides as the presence of backbone protection on the side-chain deprotected peptide prevents the formation of relatively stable folded structures that can complicate HPLC purification.1 11... 

Cleavage of peptide from the resin (with side-chain deprotection) peptides were cleaved by a mixture of TFA/H20/TIS (90 3 7 10mL-g-1 resin) for 1 h. The resin was filtered off and washed with TFA (3 x). The collected filtrates were taken to dryness in vacuo and the peptide was precipitated by ice-cold Et20. The precipitate was collected by centrifugation, resuspended in Et20 and collected by centrifugation twice. The precipitate was dried and lyophilized. 

A 25-mL round-bottom flask was charged with l-[Val-Thr(Bzl)-Val-Thr(Bzl)-DMEDA]2 (180 mg, 102 pmol) dissolved in MeOH (2 mL) and formic acid (approx. 3 mL). The flask was flushed with N2 and 10% Pd/C (102 mg) was added. The N2 atmosphere was then replaced with an atmosphere of H2. The reaction was monitored by C18 RP-HPLC. After 4-5 h, the MeOH was removed under reduced pressure and the thick, heterogeneous soln was diluted with H20 (10 mL). The pH of the soln was adjusted to approx. 7 and the catalyst filtered using a 0.22-pm acetate membrane. The soln was analyzed by analytical C18 RP-HPLC and purified using semi-preparative C18 RP-HPLC. The MeCN in the column fractions was removed under reduced pressure and the sample lyophilized to afford the side-chain deprotected peptidomimetic 3 yield 58 mg (45%) ESI-MS rn/z- [M+H]+ calcd. 1253.5 found 1254.0. 

CyCliZati°n VKLKV-D-YPLKVKL-D-YP side-chain deprotection ... 

The peptides were synthesized as large spots (diameter about 0.6 cm) at high density, which can reach up to 1.9 fimol/cm2 (32). About 1000 peptides were synthesized per 20 x 29 cm cellulose sheet. After the final side-chain deprotection step, the membrane was washed and the peptides were cleaved from the membrane (33). At this point, the peptides still remain adsorbed onto the membrane but will dissolve once a liquid is added. The peptides were then punched out with a normal single-hole puncher, and the spots were transferred into a 96-well microtiter plate. Distilled water was added in each well to dissolve the peptides. 

The TCR protein was cleaved from the resin in DCM/TFE/AcOH (3 1 1) for 3 hours. To obtain the crude protein, side chain deprotection was performed with reagent K [20] for 8 hours with an yield of 48 mg = 74%. Due to the insolubility... 

Using mass spectrometry techniques, the mass distribution of peptide mixtures can be experimentally determined and compared to the theoretical mass distribution this distribution has the shape of a beU curve, and can be calculated using various computer programs. These data provide important information on the composition of the analyzed peptide mixture. While it is not possible to verify the correct representation of each individual peptide within the nnixture, the mass distribution curve can be used to confirm the correct overall composition of the nnixture. It is also often possible to confirm the correct amino acid at a defined position of a peptide nnixture. For example, the average mass (i.e., the peak of the mass distribution bell curve) of the mixture AC-AXXXXX-NH2 (716) is sufficiently different from that of the mixture AC-YXXXXX-NH2 (808). Furthermore, an incorrect mass distribution of the peptide nnixture can indicate problems that occurred during the synthesis, such as incomplete side-chain deprotection of a particular annino acid. 

In the tert-butoxycarbonyl (Boc) strategy for solid-phase peptide synthesis, cleavage from the solid-phase and side-chain deprotection is performed with strong acids such as hydrogen fluoride. Treatment of a glycopeptide with strong acid results in partial or, in most cases, complete cleavage... 

One of the first applications of gel phase 13C NMR showed that the build up of a peptide chain and deprotection of Boc groups could be readily followed (8). An example of the gel phase 13C NMR of a peptide is shown in Fig. 1. Similarly 13 C gel phase NMR was used to evaluate and develop new side chain deprotection cocktails (9). Liebfritz and Geralt, describing the use of polyethylene and polystyrene supports, showed the general application of 13C gel phase NMR methodology in the solid phase synthesis of peptides (10,11). 

FGW Butwell, R Epton, EJ Mole, N Muzaffar, S Phillips. Deprotection studies in ultra-high load solid (gel) phase peptide synthesis. 13C NMR investigation of the efficacy of boron trifluoride-based side-chain deprotection cocktails. Innov Persp Solid Phase Synth Collect Pap Int Symp 121-132, 1990. 

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