New (1R(*),5S(*))-2-R-2,4,6,8-tetraazabicyclo[3.3.0]octane-3.7-diones containing the terminal carboxy or hydroxy group in the substituent R were synthesized by cyclocondensation of 4,5-dihydroxyimidazolidin-2-one with 1-R-ureas. Single-crystal X-ray diffraction analysis showed that 2-carboxyethyl-2,4,6,8-tetraazabicyclo[3.3.0] octane-3,7-dione crystallizes as a racemate.