Abstract: Cyclic pentapeptides are disclosed having the following formula (I)-Cyclo(-A1-A2-A3-A4-A5-)-wherein A1, A2, A3, A4 and A5 are amino acid residues. The pentapeptide has amino acid residues in positions 1-2-3 to form a &ggr;-turn, and amino acid residues in positions 3-4-5-1 to form a &bgr;-turn in combination with the &ggr;-turn. D-&agr;-amino acid residues are selected for A1, A3, and A5 and L-&agr;-amino acid residues are selected for A2 and A4. Compounds having &ggr;-turns and &bgr;-turns can be synthesized, regardless of the kinds of amino acid residues, and it is possible to synthesize compounds in which desired amino acid residues are introduced into sites of &bgr;-turn and &ggr;-turn based on their importance from the viewpoint of biological activity. The present invention is therefore available for design of compounds having biological activity.

Abstract: Presented are an oxidized-type glutathione alkyl ester represented by the formula (I). ##STR1## wherein R denotes a lower alkyl group, and a salt thereof: a method of preparing said ester which is comprised of oxidizing a reduced-type glutathione monoalkyl ester represented by the formula (II), ##STR2## wherein R is as defined above, with the air, hydrogen peroxide or iodine in an aqueous solution: and a pharmaceutical composition and method for suppression of hepatic disorders characterized in that it contains as an active constituent said ester or a pharmaceutically acceptable salt thereof.

Abstract: Pentapeptides are disclosed which are capable of regulating the function of cells of the mammalian immune and/or nervous system. Also provided are pharmaceutical compositions containing the peptides and methods of use thereof.

Abstract: A polyethylene glycol derivative of the formula ##STR1## wherein R represents a lower alkyl and n represents an optional positive integer which renders the average molecular weight of the polyethylene glycol moiety about 1,000 to 12,000, a peptide modified by said polyethylene glycol derivative and a method for production thereof. The polyethylene glycol derivative (I) is capable of modifying the guanidino groups in peptides. The peptides modified by the polyethylene glycol derivative (I) are extremely stable, are considerably delayed in biological clearance (i.e. the durability is extended) and exhibit their physiological activities effectively over the long period.

Abstract: In a process for the solid phase synthesis of a polypeptide containing at least one serine residue, the improvement comprising temporarily protecting the side chain of the serine residue with a protecting group which is removed immediately following the addition of the serine to the peptide chain.

Abstract: In solid phase peptide synthesis, resin-bound peptide is treated with hydrogen fluoride so as to cleave the peptide from the resin and form a first mixture of peptide, hydrogen fluoride and resin. The resin is removed from the first mixture so as to provide a resin-free second mixture including the polypeptide and the hydrogen fluoride. The polypeptide of the second mixture then is separated from the hydrogen fluoride.