Two-step hard acid deprotection/cleavage procedure for solid phase peptide synthesis

A new two-step deprotection/cleavage procedure for t-butoxycarbonyl (Boc) based solid phase peptide synthesis is reported. First the protective groups are removed from 4-(oxymethyl)-phenylacetamidomethyl (PAM) resin attached peptide with the weak hard acid, trimethylsilyl bromide-thioanisole/trifluoroacetic acid (TFA). In the second step, the peptide is cleaved from the resin with a stronger hard acid such as trimethylsilvl trifluoromethanesulfonate in TFA or with HF. The method is also shown to deformylate Nⁱⁿ-formyltryptophan moiety efficiently. The usefulness of this procedure for practical solid phase peptide synthesis is demonstrated by comparison with other deprotection methods in the synthesis of urotensin II and human endothelin.     

Quantitative structure–activity relationship (QSAR) study of elastase substrates and inhibitors

One hundred Suc-X-Y-Ala-pNA peptides (SUC: succinyl, pNA: p-nitroanilide, X, Y: Gly, Ala, Val, Leu, Ile, Phe, Pro, x-aminobutyric acid, norvaline, norleucine) were synthesized and their reaction constants with porcine pancreatic elastase (K_m, K_cat and K_cat/K_m) were determined. These reaction constants were quantitatively analyzed using the Free–Wilson/Fujita–Ban method. The contribution of amino acid side chains to the reaction constants K_m, K_cat and K_cat/K_m), expressed logarithmically, was found to be additive. On the other hand, 19 elastase inhibitors of the general formula CF₃CO-X-Y-Ala-pNA (X,Y: ten amino acids) were synthesized, and their inhibition constants were compared with the Michaelis constant for the corresponding substrates and analyzed using free-energy-related substituent constants. In the analysis of amino acid side chains in the Y position, the K_i value of the inhibitor was generally correlated to the K_m value of the substrate, which corresponded to the inhibitor, thus confirming the validity of the equation This study may serve as a prototypical approach to unraveling structure–activity relationships of peptide substrates and inhibitors of medicinal or agricultural importance.     

A retrospective study on the patterns of sequential fluctuation of serum alpha-fetoprotein level during progression from liver cirrhosis to hepatocellular carcinoma

The patterns of sequential fluctuation of serum alpha-fetoprotein levels were analysed in 218 patients with liver cirrhosis in whom the serum alpha-fetoprotein levels were regularly and serially measured for more than 1 year. In the group of patients with persistently abnormal high values (greater than 50 ng/mL) over a follow-up period of more than 1 year, the incidence of the subsequent development of hepatocellular carcinoma was statistically and significantly higher (44%) compared to the other groups which showed normal (less than 20 ng/mL) or low abnormal levels (21-50 ng/mL) (16%), and transient abnormal high levels (greater than 50 ng/mL for a period of less than 1 year, mostly within 5 months) or fluctuated repeatedly between normal and transient abnormal high levels (23%). Hepatocellular carcinoma developed in 48 patients more than 2 years after the diagnosis of liver cirrhosis, and the fluctuating patterns of serum alpha-fetoprotein levels were analysed in these patients. The serum alpha-fetoprotein levels in 10 of these 48 patients stayed below 50 ng/mL until about 2.0-10.0 months before the detection of hepatocellular carcinoma and then increased steadily until the time of hepatocellular carcinoma detection. In these 10 patients, the monthly increasing ratios were approximately 1.6-4.8 times the previous values.