1. Solid-phase synthesis of protected peptides using new cobalt(III) ammine linkers
B E Arbo, S S Isied Int J Pept Protein Res. 1993 Aug;42(2):138-54. doi: 10.1111/j.1399-3011.1993.tb00490.x.
Cobalt(III) ammine complexes of the type cis-[CoL4(4-AMB)O-AA-Boc](CF3SO3)2, where L4 = bisethylenediamine (en)2 or tetraammine (NH3)4, and 4-AMB = 4-(aminomethyl)benzoic acid, have been synthesized and used as linkers to polystyrene resins for solid-phase synthesis of protected peptides. Boc/t-Bu-protected [Leu5]enkephalin was assembled on the two different Co(III) resins, and then cleaved from the resins by reduction of the Co(III) center in 93-96% yield. HPLC-purified protected [Leu5]enkephalin was obtained in 67-69% overall yield and characterized by amino acid analysis and 1H NMR. Stepwise synthesis on the Co(en)2-resin was also used in the assembly of Boc-Asp(OcHex)-Arg(Mts)-Gly-Asp(OcHex)-Ala-Pro-Lys(2Cl-Z)-Gl y-OH, a sequence from collagen alpha 1 Type 1. The protected peptide was cleaved from the Co(III) resin in 74% yield, and the HPLC-purified nonapeptide was characterized by amino acid analysis, 1H NMR and liquid secondary-ion mass spectrometry (LSIMS). New routes are described for the synthesis of isomerically pure Co(III) anchor complexes. The Co(III) resins were found to be compatible with both the tert-butyloxycarbonyl (Boc) and the 9-fluorenylmethoxycarbonyl (Fmoc) N alpha-protecting group strategies used in solid-phase peptide synthesis.
2. Fmoc-based solid-phase synthesis of GPR54-agonistic pentapeptide derivatives containing alkene- and fluoroalkene-dipeptide isosteres
Kenji Tomita, Tetsuo Narumi, Ayumu Niida, Shinya Oishi, Hiroaki Ohno, Nobutaka Fujii Biopolymers. 2007;88(2):272-8. doi: 10.1002/bip.20676.
Fmoc-protected Phe-Gly-type (Z)-alkene dipeptide isostere (ADI) and (E)-fluoroalkene dipeptide isostere (FADI) were synthesized and applied to Fmoc-based solid-phase peptide synthesis (SPPS). These cis-peptide bond mimetics were introduced into a bioactive pentapeptide [H-Amb-Phe-Gly-Leu-Arg-Trp-NH(2); Amb = 4-(aminomethyl) benzoic acid], which has potent GPR54 agonistic activity. The resulting pentapeptide derivatives showed low GPR54 agonistic activity, as compared with the parent peptide and (E)-ADI-containing derivative. This suggests that the trans-amide conformer of Phe-Gly peptide bond of the parent peptide would be significantly important for bioactivity. Contrary to our expectations, a (Z)-FADI-containing derivative exhibited essentially no activity, revealing the necessity of critical validation of FADI-bioisosterism.
