Pteridines. Part XLI. Synthesis and properties of 6,7,8-trimethyl-4-thiolumazine

✍ Scribed by Walter Hübsch; Wolfgang Pfleiderer

• Book ID: 102254451
• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: German
• Weight: 344 KB
• Volume: 72
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19890720414

✦ Synopsis

The first representative of the &substituted 4-thiolumazine series has been synthesized. In a sequence of reactions, 4,6-dichloropyrimidin-2-( 1 H)-one (1) is first converted into 4-chloro-6-(methylamino)pyrimidin-2( 1H)one (6), then the Cl-atom displaced by the thioxo group ( +7) followed by a coupling reaction with 4-chlorophenyldiazonium chloride to introduce the necessary N-function into the 5-position ( + 9; Scheme I ) . Reduction of the p -chlorophenylazo group leads to the 6-(methlyamino)-4-thiouracil-5-amine (10) which on condensation with diacetyl gives 6,7,8-trimethyl-4-thiolumazine (8). The physical properties of 8 are compared with the 2-thio analog and 6,7,8-trimethyllumazine indicating that 8 possesses the highest acidity and the longest UV absorption.

9. 5-Amino-6-(methylumino)-4-thioxopyrimidin-2(I H)-one (10).

In 20% aq. (NH4),S soh. (2.1 g, 7.1 mmol) is heated in an autoclave to 120" for 2 h. The precipitate is collected after cooling and washed with CHCI, and the filtrate extracted twice with CHCI,. The aq. filtrate is evaporated and the residue recrystallized together with the first precipitate from 1~ HCI (50 ml) with charcoal: colourless crystals, 0.75 g (46%). M.p. > 250" (dec.). Anal. calc. for C5H,N,0S.HCI.H20 (236.7): C 26.49, H 4.89, N 24.72; found: C 26.34, H 5.05, N 24.48.

Concentration of the filtrate to half of its volume and addition of conc. NH, to pH 6 yielded 0.24 (19%) of the free base 10 as brownish solid.