1.Solid-phase synthesis and spectroscopic studies of TRH analogues incorporating cis- and trans-4-hydroxy-L-proline.
Stavropoulos G1, Karagiannis K, Vynios D, Papaloannou D, Aksnes DW, Age Frøystein N, Francis GW. Acta Chem Scand. 1991 Nov;45(10):1047-54.
An efficient solid-phase synthesis of the TRH analogue Glp-His(Nim-Trt)-Hyp-OH is described. Na-Fmoc protected amino acids and DCC/HOBt activation were employed. The bulky and mild-acid-sensitive 2-chlorotrityl resin, utilised as the solid support, completely suppressed dioxopiperazine formation. The tripeptide is a key intermediate in the synthesis of TRH analogues incorporating cis- and trans-4-hydroxy-L-proline. The tripeptide was converted, with inversion of configuration at C-4 of the Hyp residue, to Glp-His(Nim-Trt)-cHyp lactone in the presence of triphenylphosphine-diethyl azodicarboxylate (TPP-DEAD). One-pot MeOH-TPP-DEAD transesterification of the lactone, followed by Nim-detritylation, provided Glp-His-cHyp-OMe. This ester gave the corresponding amide and acid on ammonolysis and saponification, respectively. A high-field 1H NMR investigation of Glp-His-cHyp-OH and its diastereomer Glp-His-Hyp-OH, obtained by Nim-detritylation of the key tripeptide, showed that the configuration at C-4 of the prolyl residues is critical for the determination of the preferred three-dimensional structure of the molecules.
2.Solution synthesis of the glyco-hexapeptide sequence of the human oncofetal fibronectin defined by monoclonal antibody FDC-6.
Gobbo M1, Biondi L, Filira F, Rocchi R. Int J Pept Protein Res. 1991 Nov;38(5):417-27.
The glyco-hexapeptide sequence H-Val-(GalNAc-alpha)Thr-His-Pro-Gly-Tyr-OH, was synthesized in solution by the segment condensation procedure and the stepwise procedure. A peracetylated, O-galactosaminyl threonine derivative was used for incorporating the glycosylated amino acid residue into the peptide chain. A consistent racemization occurred during the acylation of H-His-Pro-Gly-Tyr(Bzl)-OBzl with Z-Val-[GalNAc(Ac)3-alpha]Thr-OH by the BOP-HOBt procedure and the D-allothreonine containing glyco-hexapeptide was isolated in about 20% yield. Stepwise elongation of the C-terminal tetrapeptide with Fmoc-[GalNAc(Ac)3-alpha]Thr-OH and Z-Val-OH, in the presence of the same coupling reagents, yielded the L-threonine containing diastereoisomer without detectable racemization. A side product, the Nim-ethoxycarbonylated hexapeptide derivative, formed during the EEDQ-mediated condensation of Fmoc-[GalNAc(Ac)3-alpha]Thr-OH with the C-terminal tetrapeptide, was isolated and characterized.
3.A 'conovenomic' analysis of the milked venom from the mollusk-hunting cone snail Conus textile--the pharmacological importance of post-translational modifications.
Bergeron ZL1, Chun JB, Baker MR, Sandall DW, Peigneur S, Yu PY, Thapa P, Milisen JW, Tytgat J, Livett BG, Bingham JP. Peptides. 2013 Nov;49:145-58. doi: 10.1016/j.peptides.2013.09.004. Epub 2013 Sep 18.
Cone snail venoms provide a largely untapped source of novel peptide drug leads. To enhance the discovery phase, a detailed comparative proteomic analysis was undertaken on milked venom from the mollusk-hunting cone snail, Conus textile, from three different geographic locations (Hawai'i, American Samoa and Australia's Great Barrier Reef). A novel milked venom conopeptide rich in post-translational modifications was discovered, characterized and named α-conotoxin TxIC. We assign this conopeptide to the 4/7 α-conotoxin family based on the peptide's sequence homology and cDNA pre-propeptide alignment. Pharmacologically, α-conotoxin TxIC demonstrates minimal activity on human acetylcholine receptor models (100 μM, <5% inhibition), compared to its high paralytic potency in invertebrates, PD50 = 34.2 nMol kg(-1). The non-post-translationally modified form, [Pro](2,8)[Glu](16)α-conotoxin TxIC, demonstrates differential selectivity for the α3β2 isoform of the nicotinic acetylcholine receptor with maximal inhibition of 96% and an observed IC50 of 5.
4.Solid-Phase Total Synthesis of Bacitracin A.
Lee J1, Griffin JH, Nicas TI. J Org Chem. 1996 Jun 14;61(12):3983-3986.
An efficient solid-phase method for the total synthesis of bacitracin A is reported. This work was undertaken in order to provide a general means of probing the intriguing mode of action of the bacitracins and exploring their potential for use against emerging drug-resistant pathogens. The synthetic approach to bacitracin A involves three key features: (1) linkage to the solid support through the side chain of the L-asparaginyl residue at position 12 (L-Asn(12)), (2) cyclization through amide bond formation between the alpha-carboxyl of L-Asn(12) and the side chain amino group of L-Lys(8), and (3) postcyclization addition of the N-terminal thiazoline dipeptide as a single unit. To initiate the synthesis, Fmoc L-Asp(OH)-OAllyl was attached to a PAL resin. The chain of bacitracin A was elaborated in the C-to-N direction by sequential piperidine deprotection/HBTU-mediated coupling cycles with Fmoc D-Asp(OtBu)-OH, Fmoc L-His(Trt)-OH, Fmoc D-Phe-OH, Fmoc L-Ile-OH, Fmoc D-Orn(Boc)-OH, Fmoc L-Lys(Aloc)-OH, Fmoc L-Ile-OH, Fmoc D-Glu(OtBu)-OH, and Fmoc L-Leu-OH.
