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1.
A stereospecific synthesis of the 2′-deoxy analogue of showdomycin, 2-(2′-deoxy-β--ribofuranosyl)-maleimide, from 2,5-anhydro--glucitol is described. 相似文献
2.
The synthesis of 7-(β--ribofuranosyl)-4-amino-5H-pyrrolo[3,2-]pyrimidine (9-deazaadenosine) is described. It involves base-catalyzed cyclization of N-carboethoxyenamine to give β- and α-ribosylated 3-amino-2-cyanopyrroles and , respectively, followed by a one-step conversion to the desired pyrrolo[3,2-]pyrimidine system. 相似文献
3.
Synthesis of 2-Substituted Imidazole Nucleosides Condensation of the trimethylsilyl derivatives of 2-substituted diethyl and dimethyl imidazole-4,5-dicarboxylates ( 3–5 and 7–9 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D -ribofuranose ( 2 ) in the presence of trimethysilyl trifluoromethanesulfonate provided the 2-substituted diethyl and dimethyl 1-(2′,3′, 5′-tri-O-benzoyl-β-D -ribofuranosyl)imidazole-4, 5-dicarboxylates 10–15 . These were treated with ammonia to afford the 2-substituted 1-(β-D -ribofuranosyl)imidazole-4,5-dicarboxamides 16–21 . Treatment of 2-methyl-( 16 ) and 2-ethyl-1-(β-D -ribofuranosyl)imidazole-4,5-dicarboxamide ( 17 ) with fuming nitric acid in oleum at ?30° yielded the nitric acid esters 23 and 24 . Besides the esterification of the sugar hydroxyl groups one H-atom of the imidazolecarboxamide function at C(5) in these nucleosides was also substituted by the NO2 group. The conformations in solution of 16 and 23 have been determined by 1H- and 13C-NMR. spectroscopy. These studies indicate that the nucleosides exist in dimethyl-sulfoxide solution preferentially in the S-gg-syn-conformation ( 16 ) and N-gt-conformation ( 23 ). In the crystal structure of nucleoside 23 , the ribose was found to be in the O(1′)endo, C(1′)exo twist conformation. The conformation about C(4′), C(5′) is gauche-trans and the molecule exists in the syn form. 相似文献
4.
Claudine Augé Serge David Cécile Mathieu Christine Gautheron 《Tetrahedron letters》1984,25(14):1467-1470
Glycosidation of disaccharides I and III with a system of five immobilized enzymes gave excellent yields of trisaccharides -Gal-(1→4)--GlcNAc-(1→6)--Gal ¦ the I(Ma) determinant ¦ and -Gal-(1→4)--Glc-NAc-(1→3)--Gal, on the milimole scale. 相似文献
5.
Hirokazu Morisawa Takashi Utagawa Takeshi Miyoshi Fumihiro Yoshinaga Akihiro Yamazaki Koji Mitsugi 《Tetrahedron letters》1980,21(5):479-482
An enzymatic transarabinosylation between 2-chlorohypoxanthine and 1-β--arabinofuranosyluracil gave 9-β--arabinofuranosyl-2-chlorohypoxanthine which was chemically converted to 9-β--arabinofuranosylguanine and its derivatives. 相似文献
6.
3-Methylisoguanosine () has been synthesized from 5-(cyanomethylamino)-1(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)imidazole-4-carboxamide () through the carbonitrile (). 相似文献
7.
Nucleophile(s) almost exclusively added from the equatorial side of 2-nitro-β--2-enopyranoside and the axial side of 2-nitro---1-enitol. On the other hand, methoxide and -butyl peroxide ions approached from the equatorial side of 2-nitro-α--2-enopyranoside, whereas methanol and hydrogen peroxide ion from the axial side. 相似文献
8.
The β (1 → 3) -linked disaccharide was synthesized from -galactose and a -galactosamine unit with a watersoluble amide spacer. This represents the hapten of T-antigen and, when coupled to a protein, is suitable for use as an artificial antigen. Other O-β--galactosylated derivatives of galactosamine were synthesized. 相似文献
9.
Two novel nucleosides, mycalisines A and B, have been isolated from a marine sponge and their structures elucidated as 4-amino-5-cyano-7-(3--methyl-5-deoxy-β-D--pent-4-enofuranosyl)-pyrrolo[2,3-]pyrimidine and 5-cyano-7-(3--methyl-5-deoxy-β-D--pent-4-enofuranosyl)-pyrrolo[2,3-]pyrimidine-4-one, respectively. Both compounds inhibit cell division of fertilized starfish eggs. 相似文献
10.
13C-NMR spectral data on 6-aminohexyl glycosides of -β--galactopyranosyl-2-acetamido-2-deoxy-β--glucopyranose are pr 相似文献
11.
《Tetrahedron letters》1987,28(33):3809-3812
The primary hydroxyl groups of α--glucose and methyl-α--glucoside were selectively esterified by treating the free sugars with -acylthiazolidine-2-thiones, thus affording respectively 6--acyl--glucopyranoses and methyl-6--acyl-α--glucopyranosides in high yields. This new reaction is compared with our previous synthesis of 1--acyl-β--glucopyranoses from β--glucose and interpreted in terms of anomeric effect. 相似文献
12.
G.B. Marini-Bettolo M. Nicoletti I. Messana C. Galeffi J.D. Msonthi W.A. Chapya 《Tetrahedron》1985,41(4):665-670
From rhizome of two diglucosides were isolated: hypoxoside, (1), and a new one, the 0,0-β,β-di-D-glu- copyranoside of 1-(4hydroxyphenyl)-3-(4hydroxyphenyl)-1,4-pen- tadiene, (2), named nyasoside. 相似文献
13.
Felix H. Cano Concha Foces-Foces Manuel Bernabe Jesus Jimenez-Barbero Manuel Martin-Lomas Soledad Penades-Ullate 《Tetrahedron》1985,41(18):3875-3886
X-Ray and 1H N.M.R. studies on pyranoid rings 1,2--fused to dioxolane rings in acetylated -gluco- and --galactopyranose derivatives demonstrate that the configuration of the dioxolane ring influences the conformation of the pyranoid ring in the -gluco but not in the -galactopyranose series. The crystal structure of 3,4,6-tri--acetyl-1,2--(R)--(l-cyano-ethylidene)-α--glucopyranose () and 3,4,6-tri--acetyl-1,2--()-(1-cyano-ethylidene)-α--galactopyranose ()have been determined by X-ray analysis. Lattice parameters for are a=20.6021 (11), b=8.0438 (2), c=5.5541 (1) Å and β= 95.588 (3)° for a cell with P21 symmetry. These parameters for are a=20.3361 (7), b=10.0907 (2), c=18.9115 (5) Å, β =112.399 (2)°, C2, with two crystallographycally independent molecules. The conformation of the pyranoid ring in both compounds can be described as flattened 4C1 and that of the dioxolane ring as distorted E1. The importance of the torsion angles for describing problems of configuration is remarked and the use of relative configurational angles is stressed. The 1H N.M.R. spectra of and and 3,4,6-tri--acetyl-1,2-O-(S)- and (R)-ethylidene-α--glucopyranose ( and ), 3,4,6-tri-O-acetyl--1,2-O-(S)- and ()-ethylidene-α--galactopyranose ( and ), and 3,4,6-tri--acetyl-1,2--()-and ()-benzylidene-α--glucopyranose ( and ) have been analyzed by using iterative computer methods and N.O.E. measurements. The results indicate that the major solution conformation of the pyranoid ring of the derivatives in the -gluco series , and may be described as flattened 4C1 and that of and as 25. The major solution conformation of the pyranoid ring in all compounds in the -galacto series (,,,) may be described as flattened 41. 相似文献
14.
A stereoselectivity in an intramolecular cycloaddition of the olefinic -quinodimethanes 13 and 23 generated from the thermolysis of optically active 4β-[2-(4-methoxybenzocyclobutenyl)ethyl] -5α-methoxymethyl-3-phenyl-thio-methylenefuran-2-ones 12 and 22, respectively, is studied and a stereoselective synthesis of (+)--4,5-( 4-methoxybenzo) -1β,7aβ-(2α-methoxymethyl-5-oxofuro)hydrindane 1 is also described. 相似文献
15.
The synthesis of the first examples of Class II mesoionic xanthine nucleosides is described. Tri-O-acetylribofuranosylaminothiazole is cyclized by condensation with bis (2,4,6-tri-chlorophenyl) malonate and the resultant product is de-protected to yield (8-β--ribofuranosyl-5-hydroxy-7-oxothiazolo [3,2-a] pyrimidinium hydroxide); the glucosyl derivative is prepared in a similar manner. 相似文献
16.
Treatment of methyl 3,5-dideoxy-β---pentofuranoside with the Ph3P-CCl4 reagent gave none of the expected 2-chloro derivative but a mixture of l→2 linked oligosaccharides, , with some higher homologues, terminated by αa 2-chloro-2,3,5-trideoxy-α---pentofuranosyl unit at the non reducing end. 相似文献
17.
The condensation of 4-acetamido-3-cyanopyrazolo[3,4-d]pyrimidine ( 5 ) with crystalline 2,3,5-tri-O-acetyl-β- D -ribofuranosyl chloride ( 6 ) has furnished a good yield of nucleoside material ( 7 ) which on treatment with sodium methoxide in methanol provided a high yield of nucleoside which was subsequently established as methyl 4-amino-1-(β- D -ribofuranosyl)pyrazolo[3,4-d]-pyrimidine-3-formimidate monohydrate ( 11 ). The formimidate function of 11 was found to be highly reactive and 11 was readily converted into the corresponding carhoxamidine ( 8 ), carboxamidoxime ( 14 ) and carboxamidrazone ( 15 ) when treated with the appropriate nucleophiles. Treatment of the imidate ( 11 ) with sodium hydrogen sulfide gave a high yield of the thiocarboxamide ( 12 ) which was then readily converted into 4-amino-3-cyano-1-(β- D -ribofuranosyl)pyrazolo[3,4-d]pyrimidine ( 16 ). Aqueous base transformed 11 into 4-amino-1-(β- D -ribofuranosyl)-pyrazolo[3,4-d]pyrimidine-3-carboxamide ( 10 ) while more vigorous basic hydrolysis provided the corresponding carboxylic acid ( 9 ) in nearly quantitative yield. Decarboxylation of 9 proceeded smoothly in hot sulfolane to provide the known 4-amino-1-(β- D -ribofuranosyl)pyrazolo[3,4-d]pyrimidine ( 13 ) in 68% yield which unequivocally established the site of ribosylation and anomeric configuration for all nucleosides reported in this investigation. 相似文献
18.
A series of 6-substituted purine nucleosides have been synthesized in moderate yield by the nickel catalyzed cross coupling reaction between alkyl- and aryl- Grignard reagents and 2′,3′,5′-tris-0-(t-butyldimethylsilyl)-9-β--ribofuranosyl-6-chloropurine. 相似文献
19.
The preparation of methyl 3-0-tert-butyldiphenylsilyl-2,4-dideoxy-β--- hexopyranoside, a key chiral intermediate for mevinic acids, and its elaboration into four mevinate analogues are described. 相似文献
20.
Direct ring-opening of the epoxide ring in 1-(5′--trityl-2′,3′-anhydro-β-D-lyxo-furanosyl) uracil (1) by lithium acetylide or vinylmagnesium bromide/cuprous iodide affords the corresponding 5′--trity]-3′--substituted-3′-deoxy--uridine species. 相似文献