Abstract: The present invention is directed to linkers based on ester bond linkages, especially iminodiacetic acid ester bond linkages, for use in solid phase peptide synthesis. In particular, the invention is directed to cleavable linkers that can release peptide from the solid phase support under relatively mild conditions by formation of a diketopiperazine or other cyclic structure, such that the cyclic structure remains on the solid phase support, and, in a second cleavage, under more stringent conditions of high pH. The invention is further directed to solid phase supports prepared with multiple cleavable linkers, including a linker that is cleaved by formation of a cyclic product. One such second linker is an ester of hydroxymethylbenzoic acid, or esters formed by carboxy groups of aspartic or glutamic acid.

Abstract: Novel peptide analogs of the serum thymic factor are disclosed, structurally modified, in comparison with the natural substance, both in their N-terminal and C-terminal parts and inside the amino-acid sequence, corresponding to the general formula IA-Gly-Gly-Ser-Asn-B-C-NH-R (I),in which A is pGlu, Gln, Ala-Lys-Ser-Gln, pGlu-Ala-Lys-Ser-Gln or Gln-Ala-Lys-Ser-Gln, B and C are Gly, Phe, Leu, Ala or a direct bond, and R is H, an alkyl with 1 to 6 carbon atoms or a 2-phenylethyl. Depending upon their chemical structure, the subject thymic factor analogs possess either agonistic (immunostimulative) or antagonistic (immunosuppressory) properties.