Glykoside von Heterocyclen. LII. Synthese und spektrale Eigenschaften von Ribofuranosiden des Pyridons‐(2), Pyridazons‐(3) und deren Schwefelisologen

Abstract

Ausgehend von den benzoylierten Ribofuranosiden des Pyridons‐(2) 5 und Pyridazons‐(3) 6 gelang die Synthese der Ribofuranoside des Thiopyridons‐(2) 3 und Thiopyridazons‐(3) 4 durch Thionierung mittels Phosphor(V)‐sulfid in α‐Picolin bzw. Pyridin. Die Ribofuranoside 1, 2, 3 und 4 wurden UV‐, CD‐ und NMR‐spektroskopisch untersucht. Bei den nichtthionierten Verbindungen 1 und 2 wechselte das Vorzeichen der Cotton‐Effekte durch ein zum glykosidischen N‐Atom benachbartes N‐Atom. Die thionierten Verbindungen 3 und 4 zeigten bei den den UV‐Absorptionsmaxima entsprechenden Wellenlängen Cotton‐Effekte mit positivem Vorzeichen. Bei 3 trat bei 397 nm noch ein auf einen n → π*‐Übergang zurückzuführender Cotton‐Effekt mit negativem Vorzeichen auf.

S-Nucleoside photorearrangement. Access to pyridine pseudonucleosides

“…The solvent was evaporated under reduced pressure, and the residue was treated with diazomethane in methanol to give, after silica gel column chromatography (elution with hexane-acetone, 95:5), 130 mg of a mixture whose four constituents were separated on silica gel preparative TLC (benzene-ether, Irradiation of 4-(Benzylthio)pyridine (4a). 4-(Benzylthio)pyridine (4a;5 90 mg, 0.9 mmol) in 50 mL of 2-butanol was irradiated as above during 1 h. The photoproduct mixture was methylated (diazomethane, methanol) to yield, after silica gel column chromatography (elution with a hexane-acetone gradient), 4-(benzylthio)pyridine (4a; 4 mg), 4-(methylthio)pyridine [4 (R = CH3); 11 mg], and 3-benzyl-4-(methylthio)pyridine [5a (oil); 35 mg (40%); MS m/e 215 (M+•); UV Xmax 263 nm; NMR (CDC13) 8.30 (d, J = 5 Hz, 1, H-6), 8.18 (s, 1, H-2), 7.20 (m, 5, C6H5), 6.95 (d, J = 5 Hz, 1, H-5), 4.00 (s, 2, CH2), 2.40 (s, 3, CH3S)].…”

“…After addition of methanol (2 mL) and solid sodium bicarbonate (4.5 g), the solution was filtered. The reaction product was purified on a column of silica gel; elution with CHCl3-methanol (99:1) gave 486 mg of 2- MS m/e 369 (M+-)UV Xmax 245 nm (e 6000), 285 (4400); NMR 8.30 (d, 1, H-6), 7.43 (t, 1, H-4), 7.10 (d, 1, H-3), 6.90 (t, 1, H-5), 6.10 (d, J = 4 Hz, 1, H-T), 5.6-5.2 (m, 2, H-2' and H-3'), 4.5-4 (m, 3, 2 X H-5' and H-4'), 2.10 (s, 9, CH3CO).…”

“…Fractions II and III contained the amorphous 2-(methylthio)-5-(2',3'-isopropylidene-/3-D-ribosyl)pyridine [ß-3 (7 mg)] and 2-(methylthio)-5-(2',3'-isopropylidene-a-D-ribosyl)pyridine [ct-3d], mp 87-89 °C (9 mg), respectively. ß-3 (Ci4Hi9N04S): M+-found 297.1035; UV Xmax 254 nm (e 9000), 296 (3800); NMR 8.46 (br s, 1, H-6), 7.44 (d, 1, H-4), 7.16 (d, 1, H-3), 4.82 (d, J = 4.1 Hz, 1, H-T), 4.74 (q, 1, H-2'), 4.50 (q, 1, H-3'), 4.16 (m, 1, H-4'), 3.88 (d, 2,2 X H-5'), 2.55 (s, 3, CH3S), 2.00 (br s, 1, OH), 1.61 and 1.35 (2X) (s, 3, CH3).…”

“…Deacetylation of the latter (NaOMe-MeOH) gave the known ß nucleoside 6 (R = ribofuranosyl). 7 The other constituents of the mixture were separated and characterized after methylation (CH2N2), deoxyacetylation, and treatment with 2,2-dimethoxypropane (acetone, TsOH). Two anomeric pairs of isomeric pyridine pseudonucleoside acetonides 2d (9%) and 3d (5%) were obtained.…”