3-Pyridyl C-nucleoside

Recently, C-nucleoside synthesis by glycosyl free radical coupling with protonated nitrogen heterocycles started to gain impetus. Thus, photoirradiation of the l-(2,5-anhydro-D-allonoyloxy)pyridine-2-thione derivative 798 gave the D-ribofuranosyl free radical 799 that couples with substituted pyridines to give a mixture of the two anomers of 2-pyridyl C-nucleosides... 

The 1,2-diazine system of the 1,2,4-triazine C-nucleoside 801 (Section XXX,A,1) is activated by the electron-withdrawing effect of the two tri-fluoromethyl groups. Consequently, it undergoes inverse [4 -I- 2] cycloaddition with electron-rich vinyl compounds as dienophiles, affording adducts that lose nitrogen to furnish 2-pyridyl C-nucleosides such as 802 (95AP175) (Scheme 222). 

Only 2-carbamoyl-6-()8-D-ribofuranosyl)pyridine (88CPB634) and its 4-carbamoyl congener (91MI25) revealed weak to moderate antitumor activity the many other differently substituted 2-pyridyl C-nucleosides were inactive as antitumor and antiviral agents (86MI8 92HCA1613 93-JHC1245). 

There have been further reports on pyridine C-nucleosides. 4-Carbam-oyl-2-p-D-ribofuranosylpyridine 54 and 3-carbamoyl-5-P-D-xylofuranosyl-pyridinel55 have been prepared by Alderweireldt s approach (see Vol. 21, p. 211), and some 2 -deoxy-r,2 -didehydro-pyridine C-nucleosides have been prepared by base-catalyzed elimination. Addition of lithiopyridines to 2,3-C-isopropylidene-5-C-TBDMS-D-ribonolactone gives adducts such as (133), which can be reduced to p-pyridyl C-nucleosides with EtaSiH.l T Coupling of the anomeric free radical, produced by photolysis of an iV-acyl-thiohydroxamate, with pyridinium and quinolinium salts gave 2-pyridyl C-nucleosides and 2-quinolinyl systems such as (135), where P-selectivity was... 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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