The molecular structure of the free acid of guanosine 3',5'-cyclic monophosphate (cyclic GMP).

The structure of the free acid of guanosine 3',5'-cyclic monophosphate has been determined from three dimensional x-ray diffraction data collected with a GE XRD-490 automated diffractiometer. The molecule crystallizes in the orthorhobic space group P212121 with a = 17.953(17), b = 7.530(7), and c = 12.755(12) and Z = 4. The structure was solved by direct methods. The 969 independent data were defined by full matrix least-squares to a final agreement factor, RF, of .050 for FO greater than sigma (FO). The compound exists as a switterion in the solid state. N(7) of the base is protonated. The structure of the free acid is similar to that of the sodium salt. Both have the syn conformation. The puckering of the sugar rings is also similar. Small differences exist in the bond angles of the cyclic phosphate and furanose rings.