Design and synthesis of an orally active GPIIb/IIIa antagonist based on a phenylpiperazine scaffold.

The design and synthesis of an orally active LMW non-peptide GPIIb/IIIa antagonist, based on a N,N'-bisphenylpiperazine scaffold, is described. The optimal compound showed a high in vitro binding potency (pIC50 = 8.7) in combination with potent oral antithrombotic activity (30-40% inhibition of thrombus growth at 0.3-3 mg/kg) with a duration of action of > 90 min. in a hamster cheek pouch model.

Chemical synthesis of a messenger ribonucleic acid fragment: AUGUUCUUCUUCUUCUUC.

The synthesis via a phosphotriester method of the octadecaribonucleotide AUG(UUC)5 (19) is reported. The octadecanucleotide is meant to serve as a synthetic messenger in a ribosomal protein synthesizing system. A fully protected octadecamer intermediate (18a) was prepared by a block coupling procedure. For the introduction of the desired 3'-5'-internucleotide bonds a 3'-O-(2,2,2-trichloroethyl 2-chlorophenyl phosphate) function was incorporated into the monomeric building blocks which were applied in the synthesis of 18a. Monomeric and oligomeric compounds with a thus protected 3'-O-phosphotriester function can be selectively deblocked to give 3'-O-phosphodiester derivatives suitable for condensation with 5'-hydroxyl (oligo)nucleotides. Conversion of fully protected oligomers to 5'-hydroxyl derivatives, suitable for further coupling at the 5' end, was effected by selective removal of the levulinyl function at the 5' end. The fully protected octadecanucleotide 18a was deblocked with fluoride ions, followed by ammonia and acid to give the required octadecamer 19. The condensing agent 1-(2,4,6-triisopropyl-phenylsulfonyl)-3-nitro-1,2,4-triazole, which was applied to effect the formation of fully protected 3'-5'-internucleotide phosphotriester functions, may give rise to side reactions with the heterocylic bases uracil and guanine. The consequences of these side reactions for the synthesis of octadecamer 19 are reported.

Conformational analysis of the nucleotides A2'-5'A, A2'-5'A2'-5'A and A2'-5'U from nuclear magnetic resonance and circular dichroism studies.

In recent publications A2'-5'A2'-5'A was found to be an inhibitor of protein synthesis. In this research conformational analysis of the 2'-5'-linked nucleotides A2'-5'A, A2'-5'A2'-5'A and A2'-5'U is reported. The complete 1H-NMR assignment of the three compounds is given. The degree and mode of base-base stacking is extracted from coupling constant data and circular dichroic (CD) spectra at various temperatures. The 2'-5' nucleotides surprisingly show a much stronger tendency to stack than the 3'-5' compounds. At 85 degrees C A2'-5'A occurs for about 50% in stacked states. The mode of stacking is different from 3'-5'ribonucleotides where the sugar rings predominantly adopt an N conformation. A2'-5'U displays an A(S)2'-5'U(N) stacked state. In A2'-5'A 'mixed' modes of stacking, i.e. NN, NS, SN and SS, are proposed to account for the CD and NMR observations.

Analogs of (2'-5')oligo(A). Endonuclease activation and inhibition of protein synthesis in intact cells.

Synthetic analogs of (2'-5')oligo(A) were assayed for endonuclease activation in cell extracts and for inhibition of protein synthesis in intact cells. The analogs are triadenylates: (i) methylated in the terminal 3'-OH; (ii) methylated at all three 3'-OH groups; (iii) with different numbers of phosphate groups at the 5' terminus or with a methylene group between the beta- and gamma-phosphate. Only 5'-phosphorylated monomethylated analogs activate an endonuclease in cell extracts and are powerful inhibitors of protein synthesis in intact cells. The analogs with only one 5'-terminal phosphate may require addition of another phosphate for activity since the kinase inhibitor 2-aminopurine prevents endonuclease activation by this compound but not by the di- and triphosphate-terminated triadenylates. These results suggest that two terminal phosphates and one or two free 3'-OH are required for endonuclease activation and inhibition of protein synthesis. The monomethylated analogs are more active than (2'-5')pppA3 because of their resistance to degradation by cellular enzymes. Accordingly, the monomethylated analogs cause a prolonged inhibition of protein synthesis in human fibroblasts treated with nanomolar concentrations of these compounds.