Practical preparation and deblocking conditions for N-alpha-(2-(p-biphenylyl)-2-propyloxycarbonyl)-amino acid (N-a-Bpoc-Xxx-OH) derivatives

Reproducible preparations are given for salts of the following L-amino acid derivatives: Bpoc-Ala-OH, Bpoc-Arg(Mtr)-OH, Bpoc-Asn-OH, Bpoc-Asp(OtBu)-OH, Bpoc-Cys(Acm)-OH, Bpoc-Cys(S-tBu)-OH, Bpoc-Gln-OH, Bpoc-Glu(OtBu)-OH, Bpoc-Gly-OH, Bpoc-Ile-OH, Bpoc-Leu-OH, N-alpha-Bpoc-Lys(epsilon-Boc)-OH, Bpoc-Met-OH, Bpoc-Phe-OH, Bpoc-Pro-OH, Bpoc-Ser(OtBu)-OH, Bpoc-Thr(OtBu)-OH, Bpoc-Tyr-OH, Bpoc-Val-OH. A study of the deblocking of N-alpha-Bpoc peptides in dichloromethane containing 0.5% trifluoroacetic acid revealed that a rapid equilbrium is established between the first-formed monomeric alkene 2-p-biphenylylpropene and the hindered dimer 2,4-bis(p-biphenylyl)-4-methyl-1-pentene. Thioethers were found to be inefficient carbocation scavengers for the deblocking reaction. The most efficient scavengers were found to be thiophenol and benzyl mercaptan, and the following approximate reactivity order was established: benzyl mercaptan approximately thiophenol greater than indole much greater than 1,3-dimethoxybenzene approximately resorcinol greater than 1,3,5-trimethoxybenzene approximately dimethyl sulfide approximately thioanisole.

Deamidation of the asparaginyl-glycyl sequence

The deamidation of Ac-Asn-Gly-NHMe and Ac-Isn-Gly-NHMe has been studied as a model for the facile deamidation of the Asn-Gly sequence in proteins. At alkaline pH, the product in each case is an identical mixture of Ac-alpha-Asp-Gly-NHMe (approximately 22%) and Ac-beta-Asp-Gly-NHMe (approximately 78%) as determined by n.m.r. spectroscopy. Because this same ratio is obtained from both Ac-Asn-Gly-NHMe and Ac-Isn-Gly-NHMe, the postulated mechanism, that deamidation proceeds through a cyclic imide intermediate, is confirmed. Unlike peptides of aspartyl esters, cyclization does not occur under nonaqueous conditions or at low pH in aqueous solution.

New compounds: peptide derivatives of the antitumor agent N-phosphonoacetyl-L-aspartic acid

Two peptide forms of the antitumor transition state analogue N-phosphonoacetyl-L-aspartic acid (N2-phosphonoacetyl-N4-glycylglycinamidoethyl-L-asparagine and N1-glycylglycinamidoethyl-N2-phosphonoacetyl-L-isoasparagine ) have been synthesized to obtain potential medicinal agents useful as prodrugs or in a lysosomotropic carrier approach. The bridging unit, ethylenediamine, used for synthetic purposes might be of general interest.

Reexamination of sodium-liquid ammonia reduction in the peptide chemistry

Sodium-liquid ammonia reduction has been used for over 50 years for removal of benzyl-type protecting groups in peptide chemistry. Up until now a definitely blue end-point has generally been accepted for detection of the completion of reaction. Systematic investigation with model compounds has revealed that this is not only unnecessary for the complete removal of the protecting groups but also that the application of sodium in excess results in many undesired transformations which can simply be suppressed or even eliminated by optimizing the sodium consumption. Cleavage of tert.-butyloxycarbonyl group and N-C alpha bond, reduction of carboxamide groups to carbinol derivatives, transpeptidation and formation of a hydantoin derivative have been observed in model experiments by using sodium in excess.

Synthesis and catalytic activity of poly-L-histidyl-L-aspartyl-L-seryl-glycine

Poly(His-Asp-Ser-Gly) was synthesized from the fully protected tetrapeptide active ester hydrochloride, which was prepared by stepwise coupling, using pentachlorophenyl ester and mixed anhydride methods. Complete deprotection of the protected tetrapeptide polymer was achieved by using 90% trifluoroacetic acid. The free polymer was dialyzed for 24 hr using a membrane (which retains molecules with molecular weights greater than 5000). The catalytic activity was determined by studying the hydrolysis of p-nitrophenyl acetate in 0.2 M phosphate buffer (pH 7.4) at 37 degrees. The catalytic coefficient of the dialyzed polymer was found to be 138 liters/mole/min.

Synthesis of glycopeptides containing the amino acid sequence 17-23 of bovine pancreatic deoxyribonuclease

2-Acetamido-3,4,6-tri-O-acetyl-1-N-[N-(benzyloxycarbonyl-L- seryl)-L-aspart-1-oyl-(p-nitrobenzyl ester)-4-oyl]-2-deoxy-beta-D-glucopyranosylamine, 2-acetamido-3,4,6-tri-O-acetyl-1-N-[N-(benzyloxycarbonyl-L-seryl)-L-aspart-1-oy l-(L-alanine methyl ester)-4-oyl]-2-deoxy-beta-D-glucopyranosylamine, and 2-acetamido-3,4,6-tri-O-acetyl-1-N-[N-benzyloxycarbonyl)-L-aspart-1-oyl-(L-alan yl-L-threonyl-L-leucyl-L-alanyl-L-serine p-nitrobenzyl ester)-4-oyl]-2-deoxy-beta-D-glucopyranosylamine (7), which span the amino acid sequence 17-23 of bovine pancreatic deoxyribonuclease A and contain a 2-acetamido-2-deoxy-D-glucose residue, were synthesized. On treatment with lithium hydroxide, the blocked glycohexapeptide 7 gave 2-acetamido-1-N-[N-(benzyloxycarbonyl)-L-aspart-1-oyl-(L-alanyl-L-threonyl-L-le ucyl-L-analyl-L-serine)-4-oyl]-2-deoxy-beta-D-glucopyranosylamine.

Synthesis of human beta-endorphin in solution using benzyl-type side chain protective groups

A solution synthesis of human beta-endorphin (beta-EP) was carried out by condensation of protected peptide segments bearing N alpha-tert.-butyloxycarbonyl groups and benzyl-derived groups for the protection of functionalities in amino acid side chains. Five intermediate segments were assembled in a stepwise manner starting at the carboxyl terminus. Thus, the segment of sequence region (27-31) was coupled to segment (22-26) by the azide method. Segment (19-21) was incorporated into the growing chain by azide coupling, and segment (10-18) by dicyclohexylcarbodiimide coupling in the presence of 1-hydroxybenzotriazole (DDC-HOBt). Solubility problems in condensing the ensuing 22-peptide with segment (1-9) by DDC-HOBt were overcome by using a dimethylformamidephenol mixture as a solvent. Protecting group cleavage by Na in liquid NH3 was much superior to liquid HF which gave rise to many decomposition products. Homogeneous betah-EP indistinguishable from authentic material in physiochemical and biological properties, was obtained in a single preparative reversed phase liquid chromatographic step after protecting group cleavage.

Use of cyclopentyl ester protection for aspartic acid to reduce base catalyzed succinimide formation in solid-phase peptide synthesis

A study was conducted to determine the effect of amino acid sequence and aspartyl protecting group on the rate of base catalyzed succinimide formation in the solid-phase synthesis of aspartyl peptides. The peptides H-Ala-Asp-Gly-Phe-OH and H-Ala-Asp-Leu-Phe-OH were synthesized by the solid-phase method with cyclopentyl or benzyl protection for the beta-carboxyl of aspartic acid. The results showed that the cyclopentyl ester was notably less susceptible to succinimide formation by treatment with tertiary amine than was the benzyl ester, and that the difference could have significant consequences for the synthesis of the large peptides which contain reactive sequences such as Asp-Gly.

Nepsilon-(beta-Aspartyl)lysinuria in children with various pathological conditions

The isolation, identification, and quantitative determination of an unusual urinary dipeptide, Nepsilon-(beta-aspartyl)lysine, is described, as well as its synthesis. This compound was observed in children in various disease states, but without any correlation with a particular symptom. Its origin is discussed.