1.Isolation and detailed characterization of the trans-[(H2O)2FeCl4](-) anion: stabilization of novel iron(III) species by large organic cations.
James BD1, Bakalova M, Liesegang J, Reiff WM, Skelton BW, White AH. Inorg Chem. 2001 Aug 27;40(18):4617-22.
1,2-Diaminoethane (en) and FeCl3 give (enH2) [FeCl5(H2O)] (1) in concentrated HCl, extending the aquapentachloroferrate(III) series. For 1: C2H12N2Cl5OFe, orthorhombic, P2(1)2(1)2(1), a = 14.531(6) A, b = 10.772(4) A, c = 6.888(2) A, Z = 4. Diazabicyclo[2.2.2]octane dihydrochloride (DABCO-2HCl) and FeCl3 in concentrated HCl form a tetrachloroferrate(III) derivative whose subsequent ethanol treatment (restricted water access) results in the formation of a compound of composition (DABCOH2)2 [FeCl4(H2O)2]Cl3 (2). This contains the trans-[FeCl4(H2O)2](-) anion, in which the trans-Fe-O distances are 2.049(4) A. For 2: C12H32N4Cl7O2Fe, orthorhombic, Pnma, a = 16.378(3) A, b = 7.3323(6) A, c = 19.431(3) A, Z = 4. A combination of 57Fe Mössbauer spectroscopy and ac susceptibility data confirm uncanted 3D antiferromagnetic ground states with T(Néel) approximately 3.4 K for (enH2)[FeCl5(H2O)] and approximately 2.0 K for [DABCOH2]2[FeCl4(H2O)2]Cl3.
2.N-(ureidoethyl)amides of cyclic enkephalin analogs.
Ciszewska M1, Kwasiborska M, Nowakowski M, Oleszczuk M, Wójcik J, Chung NN, Schiller PW, Izdebski J. J Pept Sci. 2009 Apr;15(4):312-8. doi: 10.1002/psc.1118.
Novel N-(ureidoethyl)amides of cyclic enkephalin analogs have been synthesized. The p-nitrophenyl carbamate of 1-Boc-1,2-diaminoethane was coupled with 4-methylbenzhydrylamine (MBHA) resin. The Boc group was removed by treatment with HCl/dioxane, and the peptide chain was assembled using Boc strategy. For deprotection of amino function, HCl/dioxane was used. D-Lys or D-Orn were incorporated in position 2, and the side chains of Lys, Orn, Dab, or Dap in position 5 were protected with Fmoc group. Side chain protection was removed by treatment with 55% piperidine in DMF, and cyclization was achieved by treatment with bis-(4-nitrophenyl)carbonate to form a urea bridge. The peptide was cleaved from the resin by treatment with 45% TFA in DCM. The peptides were tested in the guinea-pig ileum (GPI) and mouse vas deferens (MVD) assays. Divers opioid activities were observed, depending on the size of the ring. In comparison with [Leu(5)]enkephalin, all peptides were more active in the GPI assay (between 125 and 12 times), and some of them were also more potent in the MVD assay.
3.p-Nitrophenoxycarbonyl derivatives of Boc-protected diaminoalkanes in the synthesis of enkephalin peptidomimetics.
Wiszniewska A1, Kunce D, Chung NN, Schiller PW, Izdebski J. J Pept Sci. 2005 Sep;11(9):579-83.
The synthesis of p-nitrophenoxycarbonyl derivatives of 1-Boc-1,2-diaminoethane, 1-Boc-1,3-diaminopropane and 1-Boc-1,4-diaminobutane is described. These derivatives were used to synthesize five peptidomimetics, analogues of enkephalin, containing alkylurea units inside the peptide chain and at the C-terminal. All syntheses were carried out in solid phase on MBHA resin. Peptidomimetics with alkylurea units inserted into the peptide chain were synthesized using the standard method employing the Boc-strategy, with TFA deprotection and HF cleavage. The analogue containing a C-terminal alkylurea unit was synthesized using the Boc-strategy, with HCl/dioxane deprotection and TFA cleavage. All of the analogues were examined for opioid activity in GPI and MVD assays. The activity of the analogue containing a C-terminal alkylurea unit was comparable to that of [Leu5]-enkephalin, while the other analogues were less active.
4.Poly-N-acrylylpyrrolidine. A new resin in peptide chemistry.
Smith CW, Stahl GL, Walter R. Int J Pept Protein Res. 1979 Feb;13(2):109-12.
Entirely beaded poly-N-acrylylpyrrolidine-co-bisacrylyl-1,2-diaminoethane-co-N-acrylyl-1,6-diaminohexane.HCl(PAP), a new resin on which to perform peptide chemistry, has been prepared by reverse phase suspension polymerization in quantitative yield. In addition to being a superior support to polystyrene, albeit readily adaptable to current techniques of peptide synthesis, its versatility has been furthur extended by the introduction and use of new peptide-to-polymer linking groups, which allow the use of the bidirectional approach to peptide chemistry. One such linkage, which connects the side chain of cysteine to PAP via an acid resistant S-carbamoyl bond, was used in a bidirectional synthesis of deamino-oxytocin. PAP solvates and swells in solvents with wide-ranging polarities, including aqueous media. Thus, peptide coupling reactions were performed in organic media of high and of low polarity as well as in aqueous solution.
