1,3,7,9-Tetramethyluric acid

The only purine-aromatic complex crystal structure published thus far is the tetramethyluric acid-pyrene structure (6). The orientation of the molecules in this complex is shown below in VIII. 

From other planar structures which have been studied, specifically planar complexes such as the tetramethyluric acid-pyrene complex, it is known that the molecules tend to stack plane to plane at a distance of about 3.4 A. (6). One unit cell dimension in this case is 6.99 A. Thus, it would be reasonable to expect the caffeine and pyrogallol molecules to be stacked with their planes roughly perpendicular to this short axis, and it would be likely that a projection of the caffeine-pyrogallol complex down this axis to the x,y plane would result in a two-dimensional picture of the complex with a small amount of distortion owing to the tilt of the planes of the molecules with respect to the x,y plane. 

Tetramethyluric acids 200, 201 and 202 14C-labelled at C(2) have been synthesized203 by methylation of [2-14C]uric acid (specific activity SlmCimmol-1) with dimethyl sulphate at pH 9 (during 22 h), in 44.9%, 4.4% and 6.3% yields, respectively, in order to study their mode of action on the genetic material204 and to elucidate their metabolic fate in caffeine-containing plants205 206 or in mammals. 

The presence of an alkyl group at N9 but with N7 free leads to the isomeric 4-chloroisouric acids.4,5-Dichloro-4,5-dihydrouric acids result from uric acids having both imidazole nitrogens alkylated, e.g. from 1,3,7,9-tetramethyluric acid." " ... 

Alkylation of uric acid with diazoalkanes has been reviewed (32JPR(134)310). With uric acid 1,3,7,9-tetramethyluric acid is produced, presumably via an intermediate alkoxy derivative (21ZPC(117)23) since 1,3,7-trimethyluric acid and 1,7,9-trimethyluric acid with diazomethane at room temperature furnished 8-methoxy-l,3,7-trimethyl and 2-methoxy-... 

FIGURE 15.12. Some PAH-trinitrobenzene crystalline complexes, (a) 1,3,7,9-tetramethyluric acid and benzo[a]pyrene (Ref. 72). 

FIGURE 15.12 (cont d). (b) Crystal structure of 1,3,7,9-tetramethyluric acid and pyrene, (c) HOMO/LUMO overlaps for PAH-TNB complexes. Shown are signs of the wave functions (not electronic charge) for the HOMO and LUMO, and the overlap of molecules observed in the crystalline state (as predicted from the HOMO/LUMO overlap of positive with positive wave functions). 

Petermann J., Baumann T.W. and Wanner H. (1977) A new tetramethyluric acid from Coffea liberica and C. dewewei, Phytochemistry 16, 620-1. 

Mold, J.D., T.B. Walker, and L.G. Veasey Selective separation of polycyclic aromatic compounds by countercurrent distribution with a solvent system containing tetramethyluric acid Anal. Chem. 35 (1963) 2071-2074. 

Subsequent studies by these workers and their collaborators suggested several interesting differences between the effects produced in plant root tips and in mammalian cells by caffeine and other methylated oxypurines. In plants methylated oxypurines, such as caffeine, theophylline, and 1,3,7,9-tetramethyluric acid are active mainly during mitosis and the Gg period of interphase (Kihlman, 1952, 1961 Kihlman and Odmark, 1965). Among the types of aberration produced, subchromatid and chromatid exchanges predominate (Kihlman, 1961, 1966). In HeLa cells Ostertag (1966) found... 

Zheng XQ, Ye CX, Kato M, Crozier A, Ashihara H (2002) Theacrine 1,3,7,9-Tetramethyluric acid synthesis in leaves of a Chinese tea, kucha (Camellia assamica var. kucha). Phytochemistry 60 129-134... 

Baumann TW, Wanner H (1980) The 1,3,7,9-tetramethyluric acid content of cupu (Theobroma grandifiorum). Acta Amazonica 10 425... 

---