S-Ribosylhomocysteine analogs containing a [4-thio]ribose ring.
ABSTRACT: The [4-thio]-S-ribosylhomocysteine (SRH) analogs containing substitution of a sulfur atom for the endocyclic oxygen were synthesized by coupling of the 4-thioribose substrates with a thiolate generated from the protected homocysteine. Coupling of the protected 1-deoxy-5-O-mesyl-S-oxo-4-thio-D-ribofuranose with homocysteinate salt gave the C4 epimers of [4-thio]-SRH at the sulfoxide oxidation level lacking a hydroxyl group at anomeric carbon. Treatment of these sulfoxides with BF3?Et2O/NaI affected simultaneous reduction to sulfide and global deprotection affording 1-deoxy-4-thio-SRH analog. Treatment of the protected 1-deoxy-S-oxo-4-thio-D-ribofuranose sulfoxide with DAST/SbCl3 resulted in the fluoro-Pummerer rearrangement to give 4-thio-?-D-ribofuranosyl fluoride. Mesylation of the latter at 5-hydroxyl position followed by coupling with homocysteinate salt and subsequent global deprotection with trifluoroacetic acid afforded [4-thio]-SRH thiohemiacetal.
Project description:Synthesis of 5''-phosphate 2'-O-ribosylribonucleosides [Nr(p)] of four common ribonucleosides, and 3'-phosphoramidites of 5''-phosphate 2'-O-ribosyladenosine and 2'-O-ribosylguanosine using the H-phosphonate chemistry is described. An additional ring protected by benzoyl groups was incorporated into the main ribosyl ring in the reaction with 1-O-acetyl-2,3,5-tri-O-benzoyl-?-D-ribofuranose in the presence of SnCl4. The obtained 2'-O-ribosylribonucleosides (Nr) were applied in the subsequent transformations with selective deprotection. Ethanolamine was applied as a very convenient reagent for selective removal of benzoyl groups. Additionally, the tetraisopropyldisiloxane-1,3-diyl (TIPDSi) group was found to be stable under these deprotection conditions. Thus, the selectively deprotected 5''-hydroxyl group of Nr was transformed into an H-phosphonate monoester which was found to be stable under the following conditions: the removal of the TIPDSi group with triethylammonium fluoride and the dimethoxytritylation of the 5''-hydroxyl function. The 5''-H-phosphonate of Nr precursors was easily transformed to the corresponding dicyanoethyl 5''-O-phosphotriesters before phosphitylation, which gave 3'-phosphoramidite units of Nr(p) in high yield. The derived phosphoramidite units were used in an automated oligonucleotide synthesizer to produce dimer Ar(p)T via the phosphoramidite approach. The obtained products were fully deprotected under standard deprotection conditions giving dimers with a 5''-phosphate monoester function. Application of an alkaline phosphatase to prove the presence of an additional phosphate group was described.
Project description:A phosphoramidite reagent of N6-(2-deoxy-D-erythro-pentofuranosyl)-2,6-diamino-1,4-dihydro-4-oxo-5-N-methylformamidopyrimidine (MeFapy-dGuo) lesions was synthesized in four steps from 2'-deoxyguanosine. Fapy nucleosides can rearrange to the pyranose form when the 5'-hydroxyl group is unprotected. The phosphoramidite was incorporated into oligonucleotides using solid-phase synthesis by adjusting the deprotection time for removal of the 5'-dimethoxytrityl group of the MeFapy-dGuo nucleotide, thereby minimizing its rearrangement to the ribopyranose. The furanose and pyranose forms were differentiated by a series of two-dimensional NMR experiments.
Project description:We report the first total synthesis of trachycladines A (10 steps, 34.2% overall yield) and B (11 steps, 35.0% overall yield) by using 5-deoxy-1,2,3-tri-O-acetyl-?-D-ribofuranose as the starting material. The critical step was the SnCl4 assisted regio- and steroselective deprotection of perbenzylated 1-O-methyl-5-deoxyribofuranose. The enzyme adenylate deaminase (EC 18.104.22.168) was successfully applied to the chemoenzymatic synthesis of trachycladines B.
Project description:The trans-2-deoxyribosylation of 4-thiouracil (4SUra) and 2-thiouracil (2SUra), as well as 6-azauracil, 6-azathymine and 6-aza-2-thiothymine was studied using dG and E. coli purine nucleoside phosphorylase (PNP) for the in situ generation of 2-deoxy-?-D-ribofuranose-1-phosphate (dRib-1P) followed by its coupling with the bases catalyzed by either E. coli thymidine (TP) or uridine (UP) phosphorylases. 4SUra revealed satisfactory substrate activity for UP and, unexpectedly, complete inertness for TP; no formation of 2'-deoxy-2-thiouridine (2SUd) was observed under analogous reaction conditions in the presence of UP and TP. On the contrary, 2SU, 2SUd, 4STd and 2STd are good substrates for both UP and TP; moreover, 2SU, 4STd and 2'-deoxy-5-azacytidine (Decitabine) are substrates for PNP and the phosphorolysis of the latter is reversible. Condensation of 2SUra and 5-azacytosine with dRib-1P (Ba salt) catalyzed by the accordant UP and PNP in Tris?HCl buffer gave 2SUd and 2'-deoxy-5-azacytidine in 27% and 15% yields, respectively. 6-Azauracil and 6-azathymine showed good substrate properties for both TP and UP, whereas only TP recognizes 2-thio-6-azathymine as a substrate. 5-Phenyl and 5-tert-butyl derivatives of 6-azauracil and its 2-thioxo derivative were tested as substrates for UP and TP, and only 5-phenyl- and 5-tert-butyl-6-azauracils displayed very low substrate activity. The role of structural peculiarities and electronic properties in the substrate recognition by E. coli nucleoside phosphorylases is discussed.
Project description:Synthesis of a "double glycosidic" phosphodiester comprising anomeric centers of two 2-amino-2-deoxy-sugars is reported. The carbohydrate epitope of Francisella lipid A modified with ?-d-galactosamine at the anomerically linked phosphate has been stereoselectively prepared and coupled to maleimide-activated bovine serum albumin via an amide-linked thiol-terminated spacer group. H-Phosphonate and phosphoramidite approaches have been explored for the coupling of 4,6-DTBS-2-azido-protected GalN lactol and peracetylated spacer-equipped reducing ?GlcN(1?6)GlcN disaccharide via phosphodiester linkage. Deprotection conditions preserving the integrity of the labile glycosidic zwitterionic phosphodiester were elaborated.
Project description:Disaccharides that contain 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) and d-glycero-d-talo-oct-2-ulosonic acid (Ko) substituted at the 8-position by 4-amino-4-deoxy-?-l-arabinopyranosyl (Ara4N) residues have been prepared. Coupling an N-phenyltrifluoroacetimidate-4-azido-4-deoxy-l-arabinosylglycosyl donor to acetyl-protected allyl glycosides of Kdo and Ko afforded anomeric mixtures of disaccharide products in 74 and 90 % yield, respectively, which were separated by chromatography. Further extension of an intermediate Ara4N-(1?8)-Kdo disaccharide acceptor, which capitalized on a regioselective glycosylation with a Kdo bromide donor under Helferich conditions, afforded the branched trisaccharide ?-Kdo-(2?4)[?-l-Ara4N-(1?8)]-?-Kdo derivative. Deprotection of the protected di- and trisaccharide allyl glycosides was accomplished by TiCl(4)-promoted benzyl ether cleavage followed by the removal of ester groups and reduction of the azido group with thiol or Staudinger reagents, respectively. The reaction of the anomeric allyl group with 1,3-propanedithiol under radical conditions afforded the thioether-bridged spacer glycosides, which were efficiently coupled to maleimide-activated bovine serum albumin. The neoglycoconjugates serve as immunoreagents with specificity for inner core epitopes of Burkholderia and Proteus lipopolysaccharides.
Project description:A chemo-enzymatic synthesis of [(5-acetamido-9-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosylonic acid)-(2-->3)-O-(beta-D-galactopyranosyl)-(1-->3)-O-(2-acetamido-2-deoxy-alpha-D-galactopyranosyl)]-l-serine acetate (1) has been accomplished by a regioselective chemical acetylation of Neu5Ac (2) to give 9-O-acetylated sialic acid 3, which was enzymatically converted into CMP-Neu5,9Ac(2) (4) employing a recombinant CMP-sialic acid synthetase from Neisseria meningitis [EC 22.214.171.124]. The resulting compound was then employed for the enzymatic glycosylation of the C-3' hydroxyl of chemically prepared glycosylated amino acid 10 using recombinant rat alpha-(2-->3)-O-sialyltransferase expressed in Spodooptera frugiperda [EC 126.96.36.199] to give, after deprotection of the N(alpha)-benzyloxycarbonyl (CBz)-protecting group of serine, target compound 1. The N(alpha)-CBz-protected intermediate 11 can be employed for the synthesis of glycolipopeptides for immunization purposes.
Project description:GM1 is a common ganglioside pentasaccharide present on mammalian cell surface. It has been shown to play important roles in cellular communications and initiation of ?-amyloid aggregation. In order to synthesize GM1, an efficient synthetic route was developed via a [3+2] strategy. The GM3 trisaccharide acceptor bearing an azido propyl group at the reducing end was prepared using the traditional acetamide protected sialyl thioglycosyl donor, which gave better stereoselectivity than sialyl donors protected with trichloroacetamide or oxazolidinone. The glycosylation of the axial 4-hydroxyl group of GM3 by the disaccharide donor was found to be highly dependent on donor protective groups. Donor bearing the more rigid benzylidene group gave low glycosylation yield. Replacing the benzylidene with acetates led to productive coupling and formation of the fully protected GM1 pentasaccharide. Deprotection of the pentasaccharide produced GM1 functionalized with the amino propyl side chain, which will be a valuable probe for biological studies.
Project description:This paper deals with the synthesis of 2-deoxy-2-C-alkyl/aryl septanosides. A range of such septanoside derivatives was synthesized by using a common bromo-oxepine intermediate, involving C-C bond forming organometallic reactions. Unsaturated, seven-membered septanoside vinyl bromides or bromo-oxepines, obtained through a ring expansion methodology of the cyclopropane derivatives of oxyglycals, displayed a good reactivity towards several acceptor moieties in C-C bond forming Heck, Suzuki and Sonogashira coupling reactions, thus affording 2-deoxy-2-C-alkyl/aryl septanosides. Whereas Heck and Sonogashira coupling reactions afforded 2-deoxy-2-C-alkenyl and -alkynyl derivatives, respectively, the Suzuki reaction afforded 2-deoxy-2-C-aryl septanosides. Deprotection and reduction of the 2-deoxy-2-alkenyl derivative afforded the corresponding 2-deoxy-2-C-alkyl septanoside free of protecting groups. The present study illustrates the reactivity of bromo-oxepine in the synthesis of hitherto unknown septanosides, branching out at C-2, through C-C bond formation with alkyl and aryl substituents.
Project description:Polychlorinated phenoxathiins (PCPTs), polychlorinated dibenzothiophenes (PCDTs), and polychlorinated thianthrenes (PCTAs) are sulfur analogues of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/DFs). Chlorothiophenols (CTPs) and chlorophenols (CPs) are key precursors for the formation of PCTA/PT/DTs, which can react with H or OH to form chloro(thio)phenoxy radical, sulfydryl/hydroxyl-substituted phenyl radicals, and (thio)phenoxyl diradicals. However, previous radical/radical PCTA/DT formation mechanisms in the literature failed to explain the higher concentration of PCDTs than that of PCTAs under the pyrolysis or combustion conditions. In this work, a detailed thermodynamics and kinetic calculations were carried out to investigate the pre-intermediate formation for PCTA/PT/DTs from radical/molecule coupling of the 2-C(T)P with their key radical species. Our study showed that the radical/molecule coupling mechanism explains the gas-phase formation of PCTA/PT/DTs in both thermodynamic and kinetic perspectives. The S/C coupling modes to form thioether-(thio)enol intermediates are preferable over the O/C coupling modes to form ether-(thio)enol intermediates. Thus, although the radical/molecule coupling of chlorophenoxy radical with 2-C(T)P has no effect on the PCDD/PT formation, the radical/molecule coupling of chlorothiophenoxy radical with 2-C(T)P plays an important role in the PCTA/PT formation. Most importantly, the pre-PCDT intermediates formation pathways from the couplings of sulfydryl/hydroxyl-substituted phenyl radical with 2-C(T)P and (thio)phenoxyl diradicals with 2-C(T)P are more favorable than pre-PCTA/PT intermediates formation pathways from the coupling of chlorothiophenoxy radical with 2-C(T)P, which provides reasonable explanation for the high PCDT-to-PCTA ratio in the environment.