In this paper, we report the isolation procedure and structural elucidation of griseolic acids B and C. Griseolic acids B and C were separated from the mother liquid of griseolic acid A by Sephadex G-10 column chromatography. The mother liquid was dissolved in water and applied on Sephadex G-10 column and developed with water. Two active fractions (griseolic acids B and C) were individually chromatographed on a column of DEAE-Sephadex A-25. After washing with water, the column was eluted with 0.3m NaCl. The active eluate was then adsorbed on a Diaion HP-20 column. The column was washed with water and eluted with 60% Me2CO. The eluate was concentrated in vacuo and then chromatographed on a Sephadex LH-20 column with water. The active eluate was concentrated in vacuo and stored at 4°C overnight to give colorless crystals. Griseolic acid B (2): C14H13N5O7; mp 160°C (dec); [α]D +13.2° (c 1.1, DMSO); fast atom bombardment mass spectra (FAB-MS) m/z 364 (M+H)+, and griseolic acid C (3): C14H15N5O7; mp 160°C (dec); [α]D -50.7° (c 1.0, DMSO); FAB-MS m/z 366 (M+H)+ were both crystalline. Griseolic acids B (2) and C (3) were both attributed to have a N-9 substituted adenine moiety in view of the UV absorption at max 256 nm in 0.01N HCl and 260 nm in 0.01N NaOH, 1H NMR and 13C NMR spectra, which included signals at 8.21 and 8.33 ppm for 1H NMR spectra 2 and 3, and 155.8 (s, C-6), 152.8 (d, C-2), 148.4 (s, C-4), 139.5 (d, C-8) and 118.6 (s, C-5) in 2 and 155.7 (s, C-6), 152.5 (d, C-2), 148.5 (s, C-4), 139.6 (d, C-8) and 118.7 (s, C-5) in 3 for 13C NMR spectra. In addition, the FAB-MS of 2 and 3 showed a fragment peak at m/z 136 corresponding to an adenine moiety. 1H NMR spectra of griseolic acids A (1), B (2) and C (3) show close similarities. On comparison of the 1H NMR spectra of 2 with that of 1, it was noted that the singlet at 4.7 ppm in 1 (representing a C-7' proton) was not present in 2, and the doublet doublets of AB type (2.78 and 3.08 ppm) appeared instead. This observation suggested that the structure of griseolic acid B (2) corresponded to 7'-deoxygriseolic acid A. In the 13C NMR spectrum of griseolic acid C (3), sp2 carbons at 97.3 and 157.7 ppm of 2 disappeared and sp2 carbons at 85.6 (or 77.9) and 35.7 ppm newly appeared as a doublet and triplet. A C-5' olefinic proton at 5.08 ppm in the 1H NMR spectrum of 2 was absent in 3; this indicated the presence of a methylene group (2.3 ppm) and a methine bearing oxygen (4.46 ppm) in 3. These spectral properties suggested that the structure of griseolic acid C (3) corresponded to dihydrogriseolic acid B. The structure of griseolic acid C (3) was deduced by X-ray analysis. Crystal data are as follows: C14H15N5O·2H2O, MW 401.4, monoclinic, P21, a=13.660(2), b=8.509(1), c=7.881(2)Å, β=106.6(1)°, V=887.9 Å3, Z=2, Dcalc=1.52 gcm-3, μ(CuKa)=1.1 mm-1. The structure was solved by MULTAN and refined. Inhibitory activities of griseolic acids A, B, C and papaverine against cyclic adenosine 3',5'-monophosphate phosphodiesterase from rat brain [EC 3.1.4.17] expressed in terms of 50% inhibition (IC50, μM) were 0.16, 0.16, 0.12 and 3.5, respectively.