Rami Kalir

Polymeric pseudocrown ethers. III. The complexation with iron(III) in phosphoric—hydrochloric acid mixtures

Abstract Polymeric pseudocrown ethers, incorporating oxyethylene and oxypropylene units, extract FeCl 4 − from mixed hydrochloric and phosphoric acids. The complexation depends on hydrochloric acid concentration and becomes efficient when the HCl concentration exceeds 4 M . The regeneration of the polymers is accomplished with water. Column tests have been shown to separate iron very efficiently from phosphoric acid, which is recovered quantitatively. In comparison, Amberlyst A-21, a weak-base anion exchanger, shows affinity for phosphoric acid, making the separation between iron and phosphorus difficult.

Synthesis of peptide substrates for porcine elastase via (4-hydroxy-3-nitro)benzylated polystyrene (PHNB)

Peptide synthesis by means of polymeric active esters was introduced recently as a new approach to the preparation of pcptides with a predetermined sequence [ 1,2] . In this technique amino acids or peptide esters possessing a free a-amino group are coupled with high molecular weight insoluble active esters of N-blocked amino acids and cross-linked hydroxyl polymers. The Nand D-blocked peptides obtained in such a reaction could be separated readily from the insoluble reagent and subsequently elongated by removal of the N-blocking group and by coupling with the insoluble polyfunctional active ester of a desired N-blocked amino acid. Although the successful preparation of several peptides was reported [ 1,2] we did not utilize the above approach routinely, as there were certain drawbacks in the physical and chemical properties of the polymeric active esters used [3]. As shown in our previous publication [4] , these difficulties were overcome by the use of (4-hydroxyl-3-nitro)benzylated polystyrene (PHNB). In this paper we describe further applications of PHNB active esters in the synthesis of several penta-, hexaand heptapeptides, designed as substrates for mapping the active site of porcine elastase [S-7] .

Toward mechanized peptide synthesis via polymeric reagents approach

Simultaneous application of high-molecular-weight active esters and polyvinylN,N- diethylbenzylamine was used as a basis for a continuous peptide synthesis via the polymeric reagents approach. Using the synthetic procedure developed, the hexapeptide Boc-L-Pro-L-Val-L-Lys[Z(p-NO2)]-L-Val-L-Tyr(Dnp)-L-Pro-OBzr1 and the tetrapeptide Boc-l-Lys[Z(p-NO2)]-L-Lys[Z(p-NO2)]-L-Arg(NO2)-L-Arg(NO2)-OBzr, corresponding to residues 19–24 and 15–18 of human ACTH, were synthesized in 63 and 70% overall yields, respectively.

Polymeric reagent synthesis of luteinizing hormone-releasing hormone

Luteinizing hormone-releasing hormone, pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2,2 was synthesized in a stepwise manner by two approaches: the use of insoluble polymeric active esters derived from (4-hydroxy-3-nitro)benzylated polystyrene and that of solubleN,N-dicyclohexylcarbodiimide. The overall yields of the syntheses were 40 and 7%, respectively. The efficiencies of the two synthetic routes, in which identical intermediate peptides were prepared, are compared.