Intramolecular Hydrogen Bonding in N6-Substituted 2-Chloroadenosines: Evidence from NMR Spectroscopy

Two forms were found in the NMR spectra of N⁶-substituted 2-chloroadenosines. The proportion of the mini-form was 11-32% of the main form. It was characterized by a separate set of signals in COSY, ¹⁵N-HMBC and other NMR spectra. We assumed that the mini-form arises due to the formation of an intramolecular hydrogen bond between the N7 atom of purine and the N⁶-CH proton of the substituent. The ¹H,¹⁵N-HMBC spectrum confirmed the presence of a hydrogen bond in the mini-form of the nucleoside and its absence in the main form. Compounds incapable of forming such a hydrogen bond were synthesized. In these compounds, either the N7 atom of the purine or the N⁶-CH proton of the substituent was absent. The mini-form was not found in the NMR spectra of these nucleosides, confirming the importance of the intramolecular hydrogen bond in its formation.

Enzymatic Synthesis of 2-Chloropurine Arabinonucleosides with Chiral Amino Acid Amides at the C6 Position and an Evaluation of Antiproliferative Activity In Vitro

A number of purine arabinosides containing chiral amino acid amides at the C6 position of the purine were synthesized using a transglycosylation reaction with recombinant E. coli nucleoside phosphorylases. Arsenolysis of 2-chloropurine ribosides with chiral amino acid amides at C6 was used for the enzymatic synthesis, and the reaction equilibrium shifted towards the synthesis of arabinonucleosides. The synthesized nucleosides were shown to be resistant to the action of E. coli adenosine deaminase. The antiproliferative activity of the synthesized nucleosides was studied on human acute myeloid leukemia cell line U937. Among all the compounds, the serine derivative exhibited an activity level (IC50 = 16 μM) close to that of Nelarabine (IC50 = 3 μM) and was evaluated as active.

The architecture of transmembrane and cytoplasmic juxtamembrane regions of Toll-like receptors

Toll-like receptors (TLRs) are the important participants of the innate immune response. Their spatial organization is well studied for the ligand-binding domains, while a lot of questions remain unanswered for the membrane and cytoplasmic regions of the proteins. Here we use solution NMR spectroscopy and computer simulations to investigate the spatial structures of transmembrane and cytoplasmic juxtamembrane regions of TLR2, TLR3, TLR5, and TLR9. According to our data, all the proteins reveal the presence of a previously unreported structural element, the cytoplasmic hydrophobic juxtamembrane α-helix. As indicated by the functional tests in living cells and bioinformatic analysis, this helix is important for receptor activation and plays a role, more complicated than a linker, connecting the transmembrane and cytoplasmic parts of the proteins.

Enzymatic synthesis of novel purine nucleosides bearing a chiral benzoxazine fragment

A series of ribo- and deoxyribonucleosides bearing 2-aminopurine as a nucleobase with 7,8-difluoro- 3,4-dihydro-3-methyl-2H-[1,4]benzoxazine (conjugated directly or through an aminohexanoyl spacer) was synthesized using an enzymatic transglycosylation reaction. Nucleosides 3-6 were resistant to deamination under action of adenosine deaminase (ADA) Escherichia coli and ADA from calf intestine. The antiviral activity of the modified nucleosides was evaluated against herpes simplex virus type 1 (HSV-1, strain L2). It has been shown that at sub-toxic concentrations, nucleoside (S)-4-[2-amino-9-(β-D-ribofuranosyl)-purin-6-yl]-7,8-difluoro-3,4-dihydro-3-methyl-2H-[1,4]benzoxazine exhibit significant antiviral activity (SI > 32) on the model of HSV-1 in vitro, including an acyclovir-resistant virus strain (HSV-1, strain L2/R).

Thermophilic phosphoribosyltransferases Thermus thermophilus HB27 in nucleotide synthesis

Phosphoribosyltransferases are the tools that allow the synthesis of nucleotide analogues using multi-enzymatic cascades. The recombinant adenine phosphoribosyltransferase (TthAPRT) and hypoxanthine phosphoribosyltransferase (TthHPRT) from Thermus thermophilus HB27 were expressed in E.coli strains and purified by chromatographic methods with yields of 10-13 mg per liter of culture. The activity dependence of TthAPRT and TthHPRT on different factors was investigated along with the substrate specificity towards different heterocyclic bases. The kinetic parameters for TthHPRT with natural substrates were determined. Two nucleotides were synthesized: 9-(β-D-ribofuranosyl)-2-chloroadenine 5'-monophosphate (2-Сl-AMP) using TthAPRT and 1-(β-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidine-4-one 5'-monophosphate (Allop-MP) using TthНPRT.

New DNA diagnostic system for detection of factor V Leiden

Use was made of allele-specific PCR to develop a highly effective DNA diagnostic system for detection of the factor V Leiden mutation in exon 10 of human factor V gene. The allele-specific primers contain a 3'-OH end nucleotide, which matches a mutant or wild-type nucleotide of the template DNA (A-allele and G-allele, respectively) and also one mismatched nucleotide near the 3'-end. The universal primers have an internal mismatch with the mutant nucleotide of the template DNA and another mismatched nucleotide at 3'-OH end. The A-allele-specific primer enables the preferential amplification of both the homozygous and heterozygous mutant alleles. The extension of the G-allele-specific primer or the universal one is inhibited in the presence of the homozygous factor V Leiden. The developed assay system allowed us to detect five patients, who are heterozygous for factor V Leiden among the 48 patients with deep venous thrombosis and pulmonary thromboembolism.

A convenient approach to the synthesis of trinucleotide phosphoramidites--synthons for the generation of oligonucleotide/peptide libraries

Trinucleotide phosphoramidites that correspond to the codons of all 20 amino acids were synthesized in high yield in 5g scale. Precursors of those amidites--trinucleotide phosphotriesters--have been prepared using the phosphotriester approach without protection of the 3'-hydroxyl function. The structures of trinucleotide phosphotriesters and intermediates were confirmed by 1H- and 31P-NMR spectra, mass-spectra and by analysis of SPDE-hydrolysates of deprotected preparations. Purity of the target products has been confirmed by test reactions. The synthons have been used for automated synthesis of oligonucleotides and corresponding libraries by a phosphite-triester approach. A 54mer, containing 12 randomized internal bases, and a 72mer with 24 internal randomized bases have been synthesized.