Synthesis of a cyclic hexapeptide with sequence corresponding to murine tumor necrosis factor-(127-132) as a novel potential antitumor agent

A cyclic hexapeptide cyclo(Lys-Gly-Asp-Gln-Leu-Ser-) 10 was synthesized stepwise in solution by acylation of peptide ester trifluoroacetates directly with preactivated Boc-amino acids using the DCC/HOBt method; the final cyclization reaction was performed using the pentafluorophenyl ester method in solution (1-4). This peptide is a cyclic derivative of murine tumor necrosis factor-(127-132) and is designed as a potential antitumor agent. The cyclic peptide 10 displayed weak cytotoxic activity on three of the four human tumor cell lines tested.

Synthesis of cyclic peptide homologs of glutathione as potential antitumor agents

Two cyclic tripeptide homologs, cyclo(Glu[Cys-beta-Ala-]-OH) 8a, and cyclo(Glu[Cys-Gaba-]-OH) 8b, were synthesized by the pentafluorophenyl ester method in solution. These cyclic peptides are cyclo homologs of glutathione and are designed as potential antitumor agents. The 1H- and 13C-n.m.r. spectral parameters of cyclo(Glu[Cys(Bzl)-beta-Ala-]-OH) 7a were measured in DMSO-d6 and a possible conformation has been proposed. The cyclic peptide 8a showed low cytotoxic activities against three human tumor cell lines: KB, HeLa, and Colo 205.

Synthesis and enzymic hydrolysis of cyclic peptides containing an anthranilic acid residue

Two cyclic peptides cyclo (Phe-MeAnt-Glyn) with MeAnt = 5-methyl-anthranilic acid residue, n = 4 (3b) and n = 6 (4b), have been synthesized in solution and their reaction with alpha-chymotrypsin analyzed. The polyglycyl chain was prepared by the phosphazo method; cyclization at the Gly-Phe site occurred in good yield using the azide method. Catalysis of the hydrolysis of peptides 3b and 4b by alpha-chymotrypsin was characterized at 37 degrees by the apparent second-order rate constants kcat/Km 0.12 and 1.15 M-1 S-1, respectively, in agreement with the usual acceleration observed upon enlargement of the size of the peptidic ring in cyclic peptides. alpha-Chymotrypsin specifically split the Phe-MeAnt amide bond in cyclopeptide 4b. This specific orientation suggests that analogous structures with a functionalized methylene group instead of the methyl substituent can be used in the design of suicide substrates for serine proteases.

A potent new dipeptide inhibitor of cell sickling and haemoglobin S gelation

A dipeptide L-lysine-L-phenylalanine is shown to inhibit both cell sickling and the gelation of solutions of sickle-cell haemoglobin. The effect on deoxyhaemoglobin solutions and gels was followed by centrifugation; a progressive inhibition of gelation was observed up to 30 mM Lys-Phe. The haemoglobin concentration at the plateau (26 g/dl) suggests that an effect might be seen in vivo if suitable concentrations of Lys-Phe (about 20 mM) can be maintained in the blood stream. Additional studies of lag time before onset of gelation support this. Oxygen dissociation curves of sickle cells showed an effect of Lys-Phe only after incubation for 3 h before measurement, the P50 decreasing from 51 mmHg (6.8 MPa) to 41 mmHg (5.5 MPa) for cells depleted of 2,3-bisphosphoglycerate. The effect of Lys-Phe on intact sickle cells was more rapid. A marked increase in the number of unsickled cells in the presence of Lys-Phe was observed after only 15 min incubation. This result, together with measurements of uptake both into the cell and onto the cell membrane shows that the compound produces a membrane-mediated antisickling effect in addition to the effect on haemoglobin in solution within the cell. The membrane effect is not due to a change in cell volume. The properties of this dipeptide may be of value in the treatment of impending and early sickle crisis.

Cyclic peptides. X. Bitter taste and chymotryptic hydrolysis of cyclic depsidipeptides containing a tryptophan residue

Four stereoisomers (I-LL, I-LD, I-DL and I-DD) of a cyclic depsidipeptide (I) containing a tryptophan and a 2-hydroxy-4-methylpentanoic acid residue were synthesized, and their taste and chymotryptic susceptibility were examined. Compound I-LL is a depsipeptide analog of a bitter principle BP-II, cyclo(-L-Trp-L-Leu-), obtained from casein hydrolyzate. All of the four stereoisomers of I are strongly bitter to taste. Another depsipeptide analog, L-aspartyl-L-2-hydroxy-3-phenylpropanoic acid methyl ester, of the sweet H-L-Asp-L-Phe-OMe showed bitter taste instead of sweet. Chymotrypsin hydrolyzed I-LL and I-LD in moderate rates, and I-DL and I-DD very slowly.

Synthesis and hydrolysis by pepsin and trypsin of a cyclic hexapeptide containing lysine and phenylalanine

1. A cyclic hexapeptide, cyclo(-Gly2-Phe2-Gly-Lys-), and the corresponding open-chain hexapeptides, Gly2-Phe2-Gly-Lys and Phe-Gly-Lys-Gly2-Phe, have been synthesized and their susceptibilities to the hydrolytic action of pepsin and trypsin were determined. 2. The cyclic peptide was hydrolyzed slowly by trypsin to a hexapeptide Gly2-Phe2-Gly-Lys, the value of the Michaelis constant for this reaction being Km equals 0.00022 M. 3. The cyclic peptide was not cleaved by pepsin at all, but Gly2-Phe2-Gly-Lys was hydrolyzed rapidly at a Phe-Phe bond; Km equals 0.0091 M. 4. The cyclic peptide inhibits the hydrolysis of Gly2-Phe2-Gly-Lys by pepsin in a linear non-competitive manner, the value of the inhibition constant being Ki equals 0.004 M.