Synthesis of 4,8-anhydro-d-glycero-d-ido-nonanitol 1,6,7-trisphosphate as a novel IP3 receptor ligand using a stereoselective radical cyclization reaction based on a conformational restriction strategy

Tethered 1,2-Si-Group Migrations in Radical-Mediated Ring Enlargements of Cyclic Alkoxysilanes: An EPR Spectroscopic and Computational Investigation

5- to 6-member ring enlargements of 3-oxa-2-silacyclopentylmethyl to 4-oxa-3-silacyclohexyl radicals were investigated by EPR spectroscopy and QM computations of model indano-oxasilacyclopentane and oxasilinanyl compounds. Both experimental and computational evidence favored a mechanism via a concerted 1,2-migration of the "tethered" Si-group. Thus, the "forbidden" 1,2-Si-group migration from carbon to carbon becomes allowed when the Si-group is "tethered". The EPR data from 3-oxa-2-silacyclopentylmethyl radicals disclosed ground state conformations having semioccupied p-orbitals close to antiperiplanar with respect to their β-Si-C bonds, but indicated Si-hyperconjugation (β-silicon effect) was insignificant in radicals. Kinetic data was obtained by the steady state EPR method for ring enlargement of indano-3-oxa-2-silacyclopentylmethyl radicals. The scope of the novel rearrangement in terms of other ring types and sizes, as well as the analogous 1,2-migration of "tethered" C-centered groups, was explored computationally.

[Development of highly nuclease-resistant chemically-modified oligonucleotides]

Chemical modification of therapeutic oligodeoxyribonucleotides (ODNs) is necessary to avoid not only degradation by endo- and exo-nucleases but also recognition by sensors such as an innate immune system. We have been developing modified nucleosides having an aminoalky linker at the pyrimidine nucleobase or sugar moiety. ODNs containing 5-N-(6-aminohexyl)carbamoyl-2'-deoxyuridine (7) were thermally stabilized about 3°C per modification and were about 160 times more stable to hydrolysis by snake venom phosphodiesterase (a 3'-exonuclease) than unmodified ODNs, but not by endonucleases. On the other hand, ODNs containing 4'-C-(aminoethyl)thymidine (14b), which was synthesized by a newly developed radical cyclization-ring-enlargement reaction by us, were 87 times more stable to hydrolysis by DNase I (an endonuclease) and 133 times more stable in 50% human serum than unmodified ODNs. The highly stereoselective synthesis of 4'-thioribonuclesides ((S)Ns) was also developed using a Pummerer reaction. Human thrombin RNA aptamer (CII-1-37) containing 4'-thiouridine and 4'-thiocytidine was obtained by SELEX with a K(d) value of 4.7 nM, while a previously known RNA aptamer (RNA-24) has a K(d) value of 85 nM. Studies of the modification pattern-RNAi activity relationships by using (S)Ns have been carried out against luciferase genes. We found that siRNAs, which have 4 residues of (S)Ns on both ends of the sense strand and 4 residues on the 3'-end of the antisense strand, were the most effective. 4'-ThioRNA is about 1100 times more stable in 50% human plasma than unmodified RNA. However, oligoribonucleotides ((SM)ONs) containing 2'-O-methyl-4'-thioribonucleosides were 9800 times more stable in 50% human plasma than unmodified RNA. Since (SM)ON duplexes were thermally more stable than unmodified ON duplexes, therefore they would be quite suitable to use for oligonucleotide therapeutics.

Stereoselective synthesis of beta-phenylselenoglycosides from glycals and rationalization of the selenoglycosylation processes

Beta-phenylselenoglycosides have been efficiently and stereoselectively synthesized by direct oxidative glycosylation of benzenselenolate (PhSe(-)) with glycals. A rationalization of the presently described beta-selectivity and the opposite alpha-selectivity reported by Danishefsky in the ring-opening of epoxy glycals with benzeneselenol (PhSeH) is proposed.

Synthesis of adenophostin A analogues conjugating an aromatic group at the 5'-position as potent IP3 receptor ligands

Previous structure-activity relationship studies of adenophostin A, a potent IP(3) receptor agonist, led us to design the novel adenophostin A analogues 5a-c, conjugating an aromatic group at the 5'-position to develop useful IP(3) receptor ligands. The common key intermediate, a D-ribosyl alpha-D-glucoside 10alpha, was stereoselectively synthesized by a glycosidation with the 1-sulfinylglucoside donor 11, which was conformationally restricted by a 3,4-O-cyclic diketal protecting group. After introduction of an aromatic group at the 5-position of the ribose moiety, an adenine base was stereoselectively introduced at the anomeric beta-position to form 7a-c, where the tetra-O-i-butyryl donors 9a-c were significantly more effective than the corresponding O-acetyl donor. Thus, the target compounds 5a-c were synthesized via phosphorylation of the 2', 3' ', and 4' '-hydroxyls. The potencies of compounds 5a-c for Ca(2+) release were shown to be indistinguishable from that of adenophostin A, indicating that bulky substitutions at the 5'-position of adenophostin A are well-tolerated in the receptor binding. This biological activity of 5a-c can be rationalized by molecular modeling using the ligand binding domain of the IP(3) receptor.

Radical Reactions with 2-Bromobenzylidene Group, a Protecting/Radical-Translocating Group for the 1,6-Radical Hydrogen Transfer Reaction

[Structure: see text] The 2-bromobenzylidene group, designed as a novel protecting/radical-translocating (PRT) group, proved to be effective for an unusual 1,6-hydrogen transfer reaction. Using this PRT group, 4-branched ribose derivatives were stereoselectively prepared.

A Systematic Study of C-Glucoside Trisphosphates as myo-Inositol Trisphosphate Receptor Ligands. Synthesis of β-C-Glucoside Trisphosphates Based on the Conformational Restriction Strategy

Beta-C-glucoside trisphosphates having a C2 side chain (3,7-anhydro-2-deoxy-D-glycero-D-gulo-octitol 1,5,6-trisphosphate, 11) and a C3 side chain (4,8-anhydro-2,3-dideoxy-D-glycero-D-gulo-nonanitol 1,6,7-trisphosphate, 12) were designed as structurally simplified analogues of a potent D-myo-inositol 1,4,5-trisphosphate (IP3) receptor ligand, adenophostin A. Construction of the beta-C-glucosidic structure, which was the key to their synthesis, was achieved by two different methods based on the conformational restriction strategy: (1) radical cyclization with a temporary connecting silicon tether and (2) silane reduction of glyconolactols having an anomeric allyl substituent. Using these methods, the target beta-C-glycoside trisphosphates 11 and 12 were successfully synthesized. A structure-activity relationship was established on a series of C-glucoside trisphosphates, including the previously synthesized related compounds, which were a C-glycosidic analogue 3 of adenophostin A, its uracil congener 5, alpha-C-glucoside trisphosphates 7-9 having a C1, C2, or C3 side chain, and the beta-C-glucoside trisphosphates 10-12 having a C1, C2, or C3 side chain. The O-glycosidic linkage of adenophostin A and its analogues proved to be replaced by the chemically and biologically more stable C-glycosidic linkage. The alpha-C2-glucoside trisphosphate 8 stimulates Ca2+ release with a potency similar to that of IP3 in spite of its simplified structure, indicating a better fit to the receptor than the beta-C-glucoside trisphosphates and also the alpha-congeners having a shorter or longer C1 side chain, which was supported by molecular modeling using the ligand binding domain of the IP3 receptor.