Lech Dudycz

Mechanism of methylation of nucleoside sugar hydroxyl groups by diazomethane in the presence of stannous chloride

Abstract Diazomethane rapidly reacts with SnCl 2 in methanol to give MeCl and Sn(OMe) 2 , both of which were isolated and identified. This reaction is the initial step in the apparent SnCl 2 - 2H 2 O-catalysed methylation of nucleosides by diazomethane. The actual catalyst, Sn(OMe) 2 , readily reacts with Bronsted acids, with exchange of ligands. For ribofuranosyl nucleosides, Sn 2+ binds to site(s) having a labile proton, the effect being particularly predominant with 5- and 6-membered cyclic structures, with the tin ion co-ordinated to the ionised hydroxyl groups of the sugar moiety. These cyclic structures account for the high reactivity of the hydroxyl groups towards Me + , as in the complexes of ribofuranosyl nucleosides with Bu 2 SnO. A similar, if not identical, mechanism operates in the case of glucopyranosides.

SYNTHESIS AND INCORPORATION OF 2'-AMINO ACID CONJUGATED NUCLEOTIDES INTO RIBOZYMES

Abstract 2′-Amino-2′-deoxyuridine ( 1 ) was conjugated with N -Fmoc protected L-amino acids. 5′- O -Dimethoxytritylation followed by 3′- O -phosphitylation afforded 3′- O -phosphoramidites 4a-d . These monomers were incorporated into ribozymes using the solid phase phosphoramidite method. The catalytic activity of these ribozymes is reported.

A 1H NMR study of the syn-anti dynamic equilibrium in adenine nucleosides and nucleotides with the aid of some synthetic model analogues with fixed conformations.

Abstract The syn-anti equilibrium about the glycosidic bond in adenosine and some related analogues was studied by means of 1H NMR spectroscopy, with the aid of several model analogues fixed in given conformations either by intramolecular bonding, or by introduction of a bulky substituent. A model unambiguously and exclusively in the syn conformation is 8-(α-hydroxyisopropyl) adenosine; while one fixed in the a n ti conformation is 8,5′-anhydro-8-oxoadenosine. A new analogue, fixed in the high an ti conformation, is 8,2′-O-isopropylidenearabinofuranosyladenine. Several additional new model compounds were synthesized and their properties are described. With the aid of these models, the syn-anti dynamic equilibrium was examined for adenosine and some related compounds in different solvent systems, and the conformer populations evaluated quantitatively. The validity of the procedure applied, and the accuracy of the results, are critically examined, and compared with findings obtained by other procedures. Available literature data on the syn-anti equilibrium in other 8-substituted adenosines are re analyzed in the light of the present results. An analysis is also presented of the interdependence of the various conformational parameters, i. e. conformation about the glycosidic bond and those of the sugar ring and exocyclic carbinol group, in adenosine and 2′,3′-O-isopropylideneadenosine.

Purine Nucleosides and Nucleotides Unequivocally in the Syn Conformation: Guanosine and 5′-GM P with 8-tert-Butyl and 8-( α-Hydroxyisopropyl) Substituents

Direct alkylation via a free radical reaction was utilized to prepare 8-tert-butylguanosine-5′- phosphate; this was dephosphorylated with alkaline phosphatase to give the parent nucleoside. The 8- (α-hydroxyisopropyl) derivatives of 5′-GMP and guanosine were prepared in an analogous manner. The foregoing products, which are necessarily in the syn conformation about the glycosidic bond because of the bulky 8-substituents (van der Waals’ radii 3.5-4 Å), were characterized by elementary analysis, UV spectra and 1HNMR spectroscopy. The changes in chemical shifts of H (1′), H (2′) and H (3′) of each of the foregoing derivatives, relative to those for guanosine and 5′-GMP, were consistent with their being in the syn conformation and, furthermore, pointed to guanosine and 5′-GMP being predominantly anti, in aqueous medium or DMSO. They also demonstrated that, contrary to the prevailing opinion, 8-bromo-5′-GMP and 8-bromoguanosine are not necessarily exclusively in the syn conformation in solution. While 8-bromoadenosine-5′-phosphate was slowly dephosphorylated by snake venom 5′-nucleoti- dase, the 8-tert-butyl and 8-(α-hydroxyisopropyl) derivatives of 5′-GMP were fully resistant to this enzyme.

Solution Conformation of Benzimidazole Nucleosides with the Aid of Model Analogues

Abstract The 4,6-dibromo-and 5,7-dibromo-derivatives of 1-β-ᴅ-ribofuranosylbenzimidazole, and the 4,6-dibromo-derivative of 1-α-ᴅ-arabinofuranosylbenzimidazole, have been synthesized by condensation of the trimethylsilylated derivative of 4,6-dibromobenzimidazole with the appropriate protected sugar in the presence of SnCl4. Application of the fusion method led to the β-ribofuranoside of 2-methyl-5,6-dichlorobenzimidazole. Two additional analogues of the biologically active ribofuranoside of 5,6-dichlorobenzimidazole, viz. the 2′,3′-O-isopropylidene and the 5′-chloro-5′-deoxy derivatives have been synthesized. Analyses of the 1H NMR spectra of the foregoing, and of previously synthesized 5(6)-mono-halogeno and 5,6-dihalogeno derivatives, were employed to determine solution conformations of these nucleosides. Conformations of the sugar rings and exocyclic groups were evaluated from vicinal proton-proton coupling constants, as for purine nucleosides. The conformation of the benzimidazole ring about the glycosidic bond was determined from the chemical shifts of the sugar protons, principally H(2′), with the aid of model analogues in fixed syn and anti conformations; and, independently, from the chemical shifts of the benzimidazole ring protons, principally H(4) and H(7). The halogenated benzimidazole ribofuranosides exhibit conformations of the sugar ring similar to those for purine β-nucleosides, but differ from the latter in their preference for the conformation syn about the glycosidic bond.

The Synthesis and Interaction of Novel GTP Derivatives with Ras Oncogene Proteins

Abstract A series of novel GTP derivatives were synthesized and screened as prob and possible inhibitors of the ras encoded G protein p21. Based on these results and the x-ray crystallographic data on p21 we synthesized a non-nucleotide guanine analog designed to interact with specific amino acid sidechains of p21.

Preparation of 1-α-D-Arabinofuranosylbenzimidazole and Its 5,6-Dichloro Derivative, and the Direct Bromination of Benzimidazole Nucleosides

Abstract Arabinofuranosyl Benzim idazole N ucleosides, Direct Bromination of Benzim idazole N ucleosides, 1H NMR Spectroscopy, Ultraviolet Spectra The 1-a-D-arabinofuranosides of benzim idazole and 5,6-dichlorobenzim idazole, analogues of the biologically active 5,6-dichloro-l-β-D-ribofuranosylbenzimidazole, have been synthesized by condensation of the trimethylsilyl derivative of the appropriate benzim idazole in the presence of SnCl4 with 1-O-m ethyl-2,3,5-tribenzoyl-a-D-arabinoside. The 5(6)-m onobrom o and the 5,6-dibrom o derivatives of 1-β-D-ribofuranosylbenzimidazole and 1-α-D-arabinofuranosylbenzimidazole were then prepared by direct bromination of the latter. With 1-β-D-ribofuranosylbenzimidazole, the initial product of bromination was a 1:1 mixture of the 5-bromo and 6 -brom o derivatives; the final product was the desired 5,6-dibromo analogue. In the case of 1-αβ-D-arabinofuranosylbenzimidazole, the initial product of bromination was the 5-(or 6 -)brom o derivative, and the 5,6-dibrom o derivative the final product. The monobrom o derivatives were easily separated from the dibrom o by chromatography on Am berlite XAD-4. Identification of all of these was based on several criteria, including detailed analyses of the 1H NMR spectra. The benzim idazole nucleoside are considerably m ore resistant to acid hydrolysis than the cor responding purine nucleosides. The effects of halogenation on the ultraviolet absorption spectra of the benzim idazole nucleosides are described.