Nucleosides 4 -thio

Purines, N-alkyl-N-phenyl-synthesis, 5, 576 Purines, alkylthio-hydrolysis, 5, 560 Mannich reaction, 5, 536 Michael addition reactions, 5, 536 Purines, S-alkylthio-hydrolysis, 5, 560 Purines, amino-alkylation, 5, 530, 551 IR spectra, 5, 518 reactions, 5, 551-553 with diazonium ions, 5, 538 reduction, 5, 541 UV spectra, 5, 517 Purines, N-amino-synthesis, 5, 595 Purines, aminohydroxy-hydrogenation, 5, 555 reactions, 5, 555 Purines, aminooxo-reactions, 5, 557 thiation, 5, 557 Purines, bromo-synthesis, 5, 557 Purines, chloro-synthesis, 5, 573 Purines, cyano-reactions, 5, 550 Purines, dialkoxy-rearrangement, 5, 558 Purines, diazoreactions, 5, 96 Purines, dioxo-alkylation, 5, 532 Purines, N-glycosyl-, 5, 536 Purines, halo-N-alkylation, 5, 529 hydrogenolysis, 5, 562 reactions, 5, 561-562, 564 with alkoxides, 5, 563 synthesis, 5, 556 Purines, hydrazino-reactions, 5, 553 Purines, hydroxyamino-reactions, 5, 556 Purines, 8-lithiotrimethylsilyl-nucleosides alkylation, 5, 537 Purines, N-methyl-magnetic circular dichroism, 5, 523 Purines, methylthio-bromination, 5, 559 Purines, nitro-reactions, 5, 550, 551 Purines, oxo-alkylation, 5, 532 amination, 5, 557 dipole moments, 5, 522 H NMR, 5, 512 pJfa, 5, 524 reactions, 5, 556-557 with diazonium ions, 5, 538 reduction, 5, 541 thiation, 5, 557 Purines, oxohydro-IR spectra, 5, 518 Purines, selenoxo-synthesis, 5, 597 Purines, thio-acylation, 5, 559 alkylation, 5, 559 Purines, thioxo-acetylation, 5, 559... 

Treatment of the allylic sulfoxide 1227 a with diisopropylethylamine (DIPEA) or of 1227 b with N-trimethylsilyldiethylamine 146 and TMSOTf 20 leads in ca. 90% yield to the quaternary amino derivatives 1228 and 1229 and HMDSO 7 [36] (Scheme 8.15). Tetramethylene sulfoxide 1230 reacts with silylated thymine 1231 in the presence of three equivalents of TMSOTf 20 to give the 4 -thio-nucleoside analogue 1232 and HMDSO 7 [37]. Other silylated pyrimidine, pyridine, and purine bases react analogously with cyclic sulfoxides to give 4 -thio-nucleoside analogues [37, 37a, 38]. 

A series of diastereomerically pure 5 -0-DMT-nucleoside 3 -0-(2-thio-l,3,2-oxathiaphospholanes) and their oxathiaphospholane ring-substituted analogues 283-294 were isolated in 80-83% yield by column chromatography on silica gel of the appropriate diastereomeric mixtures [the ratio ca 55 45 (31P NMR assay)] obtained from the reaction of 2 - A, IV- dii so p rop y I a m i n o- 1,3,2-oxathiaphospholane 279-281 with 5 - 0 -D M T- n uc I cosides 282a-d in the presence of tetrazole (phosphi-tylation), followed by addition of sulfur (Scheme 67) [105-107]. 

Scheme 67 Synthesis of diastereomerically pure 5 -0-DMT-nucleoside 3 -0-(2-thio-l,3, 2-oxathiaphospholanes) and its oxathiaphospholane ring-substituted analogues 283-294...

The subsequent cleavage of the thio-ester succinylCoA into succinate and coenzyme A by succinic acid-CoA ligase (succinyl CoA synthetase, succinic thiokinase) is strongly exergonic and is used to synthesize a phosphoric acid anhydride bond ( substrate level phosphorylation , see p. 124). However, it is not ATP that is produced here as is otherwise usually the case, but instead guanosine triphosphate (CTP). However, GTP can be converted into ATP by a nucleoside diphosphate kinase (not shown). 

A one-pot procedure for the transformation of 6-thiopurine nucleosides to 6-aminopurines was developed using DMDO as the oxidant in the presence of a stoichiometric amount of various amines <1996T6759>. For example, 6-thio-9-(2, 3, 5 -tri-0-acetyl-/3-D-ribosyl)purine was readily converted to the 6-alkylamino derivatives (6-amino, 75% yield 6-methylamino, 55% yield). Similarly, A -6-acetyl-8-thio-9-(2, 3, 5 -tri-0-acetyl-/3-D-ribosyl)adenosine was converted to A -6-acetyl-8-methylamino-9-(2, 3, 5 -tri-0-acetyl-/3-D-ribosyl)adenosine (DMDO, methylamine, CH2CI2, 25 °C, 83% yield). Less nucleophilic 2-mercaptopurine derivatives did not undergo the displacement reaction, however, and only the products of dithiane formation and desulfurization were isolated. 

The value of some nucleosides for use as flavor enhancers,1348 and the possible antiviral or antitumor activity of certain nucleosides,135 have led to the synthesis of purine nucleosides containing analogs of D-apiose in which the ring-oxygen atom of the furanose forms has been replaced.136 Monomolar p-toluenesulfonylation of 3-C-(hydroxy-methyl)-l,2-0-isopropylidene-/3-L-threofuranose (50) yielded 3-C-(hydroxymethyl)-l,2-0-isopropylidene-31-0-p-tolylsulfonyl-/3-L-thre-ofuranose (51) which, through a series of steps, was converted into either methyl 2,3-O-isopropylidene- [3-C-(hydroxymethyl)-4-thio-/3-D-... 

This Subsection deals with the preparation of 2 - and 4 -ketohexosyl-purines and -pyrimidines, which have proved to be versatile synthetic intermediates. A 5 -keto derivative of a hexofuranose nucleoside is also described. The synthesis of epoxy-, halogeno-, unsaturated, epimino-, and thio-ketonucleosides will be developed in subsequent Subsections and Sections. 

Significant stability of ketohexose nucleosides in various media has facilitated their direct transformation, leading to important structures of biological interest, such as branched-chain and rare-sugar nucleosides (for example, amino-, epimino-, thio-, and trideoxy-nucleosides). 

This article collates information on the reactivity of sugar isothiocyanates and isomeric thiocyanates, and illustrates some of the chemical properties that have contributed to the synthesis of nucleoside analogs,1719 and thio and deoxy sugars. 

In an article that collates information not extensively treated before, Z. J. Witczak (West Lafayette) describes the synthesis, chemistry, and preparative applications of monosaccharide thiocyanates and isothiocyanates the thiocyanate anion is an ambident nucleophile of great synthetic versatility in approaches to nucleoside analogs and to thio and deoxy sugars. 

RNA modification database at http //medlib.med.utah.edu/RNAmods furnishes information concerning naturally modified nucleosides in RNA (Limbach et al., 1994). After clicking Search, select individual files (pick corresponding radios under categories base type, RNA source, and phylogenetic occurrence) to be accessed, and output options (common name, structures, and/or mass values). Enter partial name (i.e., substituent name such as methyl, thio, etc.) and choose the parent base(s) from which modified nucleosides are derived (Figure 5.8). Click Search button. The tabulated search results based on selected files are returned according to the requested output options. 

We explored other thiocarbonyl derivatives including xan-thates (e.g. 19), thionoimidazolides (e.g. 20) and thio-carbonates. The last convert a glycol such as 21a via the thiocarbonate 22 and subsequent tin hydride reduction to mainly the primary alcohol 21b. The intermediate opens in such a way as to afford the more stable radical. This reaction is readily applied to nucleosides.910... 

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