acetylation to yield the flavin analogs ( 4 ) , ( 5 ) , or (6), respectively, in good yields; they can be converted into the ribityl derivatives by deacetylation.
5-Deazaribofauin ( 4 ) , R2= R'A solution of 6-[N-(tetraacetyl-~-ribityl)-3,4-~ylidino]uracil (31, R1=RZ, (2.50g, 4.7mmol) in DMF (8ml) is treated with pocl, (0.80 ml, 8.7 mmol). The mixture is allowed to stand for 30min at room temperature and for 15min at 100°C. It is then poured onto ice, adjusted to pH = 6 with ammonia at O"C, and stirred for 30min. The product is filtered off, and washed with a large volume of water. After drying over P 2 0 5 , 2.30g (91 %) of ( 4 ) is obtained. Deacetylation in 50 % saturated methanolic ammonia solution yields 1.1Og (62 %) ( 4 ) , RZ = R', which is thin-layer chromatographically and spectrally identical with authentic
5-Deaza-5-thia-1 H-riboflavin (5), R2= R'A solution of ( 3 ) , R' =R2, (3.7mmol) in CHC13 (5ml) is treated with SCl, (0.50 ml, 7.8 mmol) and stirred for 12h at room temperature. The solvent is then removed in vacuo and the residue taken up in lOml DMF. This solution is added dropwise and slowly to 100ml of a 0.1 M solution of Na2SzO4 in 0.1 M phosphate buffer (pH = 7). After complete decoloration the solution is extracted three times with 100ml CHCl3 and the CHCl, removed in vacuo. The residual oil crystallizes upon addition ofdiethyl ether;yield 1.30g (62 %) (5). Deacetylation in 20ml saturated methanolic ammonia solution affords 0.64g (44 %) ( 5 ) , R2=R'. 'H-NMR (1 N K2C03 in DzO): 6=2.05 (s, 7,8-CH3, 6H), 3.52-4.28 (m, 10-ribityl, 7H) and 6.50-6.75 ppm (6,9-CH, 2H); UV: pH=13, anion, h,,, (E)= 262 (27 720), 298 sh (8320), 3 16 nm sh (3 170); pH = 2, neutral entity, A , , , (~)=252 (18610), 280 sh (9590), and 345 nm sh (1980); pK=5.310.1. [Z 459 IE] German version: Angew. Chem. 88,475 (1976)