Lindsay, B., Almeida, A.M.P., Smith, C., Rocha, R.M., Berlinck, R.G.S. and Ireland, C.M., “6-Methoxy-7-Methyl-8-Oxoguanine, na unusual purine from the ascidian Symplegma Rubra, Journal of Natural Products, 62, 1573-1575 (1999).

A new purine derivative, 6-methoxy-7-methyl-8-oxoguanine (1) , along with 8-oxoadenine (2) and the human metabolite 3-methylxanthine (3), has been isolated from the ascidian Symplegma rubra collected on the southeastern coastline of Brazil. The structures of the three purines were established by analysis of spectroscopic data.