Mark C. Allen

Synthesis of 5- and 7-bromotryptophan and of [5-bromotryptophan9]-β-corticotrophin-(1–24)-tetracosapeptide, a highly potent corticotrophin analogue

The synthesis of 5- and 7-bromo-L-tryptophans via Fischer cyclisation of the appropriate bromophenylhydrazone of 4-acetamido-4,4-bis(ethoxycarbonyl)butanal is described. The title tetracosapeptide was synthesised using standard methods of stepwise and fragment condensation. The product was pure as judged by amino-acid analysis after acidic or enzymic hydrolysis and by high pressure liquid chromatography. In an isolated adrenal cell bioassay, the peptide had a steroidogenic potency 2.4 times that of Synacthen.

the design and synthesis of thrombin inhibitors: the introduction of in vivo efficacy and oral bioavailability into benzthiazolylalanine inhibitors

The further optimisation of the novel lead compound CGH752 (Fig. 1) is described. By introducing various substituents into the 6-position of the 3,3-dimethyltetrahydroquinoline (DMTHQS) ring we have been able to favourably affect the in vitro and in vivo activity, and the pharmacokinetics of such compounds. One of the inhibitors synthesised (CGH1484) is bioavailable and shows efficacy in animal models of thrombosis.

Tritiated peptides. Part 7. Synthesis of [2,5-3H2-His6]-β-corticotrophin-(1–24)-tetracosapeptide

The synthesis is described of β-corticotrophin-(1–24)-tetracosapeptide ‡ labelled with tritium in the histidine residue at position 6 at a specific radioactivity of 30 Ci mmol–1 by reductive dehalogenation of a protected precursor. Evidence for the integrity of the final product is provided by amino-acid analysis, column chromatography, and bioassay, supported by chemical and enzymic analytical data on the protected precursor and the derived free peptide containing di-iodohistidine.

Tritiated peptides. Part 15. Synthesis of tritium labelled biologically active analogues of somatostatin

The syntheses are described of cyclo-{[D-Trp8,Gaba12]somatostatin-(5–12)-peptide}(77), and (79)–(82) labelled singly at positions 6, 7, 8, and 11 and doubly at residues 6 and 11 to specific radioactivities of between 4.8 and 22.4 Ci mmol–1. The linear sequence (5–12) and the related cyclo-{[D-Trp8,Nag12]somatostatin-(5–12)-peptide}(78) and (83) were also prepared to specific radioactivities of 19.2 and 19.6 Ci mmol–1 respectively. The syntheses of the labelled hexapeptide cyclo-{[4-3H-Phe7,D-Trp8,Pro12] somatostatin-(7–12)-peptide}(84) and the full sequences [4-3H-Phe6,D- Trp8,D-Cys14]somatostatin (94) and [D-Trp8,4-3H-Phe11,D-Cys14]somatostatin (95) labelled at ca. 13.0 Ci mmol–1 are described. Labelling was effected by reductive dehalogenation in the presence of tritium of the fully protected precursors and the purity of the final products was assessed by amino acid analysis after acidic hydrolysis following purification by ion-exchange and h.p.l.c. as appropriate.

Tritiated peptides. Part 11. Synthesis of [4-3H-Phe6]-, [4-3H-Phe11]-, and [4-3H-Phe6,11]-somatostatin and the metabolite [des-Ala1]-somatostatin

The syntheses are described of somatostatin+ labelled with tritium singly in the phenylalanine residues at positions 6 and 11 and doubly at residues 6 and 11 to specific radioactivities of 15.5, 13.8 and 14.1 Cim mol–1, respectively, by reductive deiodination of fully-protected precursors. Cysteine residues were protected by S-trityl groups and the disulphide bridge was formed by iodine oxidation of the tritiated protected precursors. The purity of the products was assessed by acidic hydrolysis, ion-exchange and high-pressure liquid chromatography, and by enzymic digestion of the products modified by reduction and aminoethylation. The synthesis of the metabolite [des-Ala1]-somatostatin is described. The syntheses of [Phe(I)6]-, [Phe(I)11]- and [Phe(I)6,11]-somatostatin are described.

Display of fixed residues on variable cyclic scaffolds: A novel approach to peptide combinatorial library synthesis

Abstract A synthetic peptide library is described which displays three nominated residues in varied spacing around cyclic peptides. Diversity of ring size was achieved by the use of binary combinatorial synthesis, and the inclusion of hydrophilic spacer molecules. The order of residue occurrence and chirality was fully varied while duplication was avoided using a modified split-and-mix protocol.

Synthesis of (6-[4-3H]phenylalanine)-somatostatin of high specific radioactivity

Somatostatin labelled with tritium in the 6-phenylalanine residue (1a) has been synthesised via catalytic deiodination of the fully protected intermediate (2).

A model for the binding of low molecular weight inhibitors to the active site of thrombin

This paper describes the construction, validation and application of an active site model of the serine protease thrombin. Initial use was made of medium resolution X-ray crystallographic structures of thrombin complexed with low molecular weight, non-specific inhibitors to create a computationally useable active site shell of the enzyme. Molecular mechanics methods were then applied to dock known ligands into the active site region in order to derive a model that would accurately predict binding conformations. Validation of the modelling process was achieved by comparison of the predicted enzyme-bound conformations with their known, crystallographic binding conformations. The resultant model was used extensively for predictive purposes prior to obtaining confirmatory crystal data relating to a ligand possessing a novel and unexpected binding component complexed to thrombin. The data served both to confirm the accuracy of the binding site model and to provide information for the further refinement of the model.