A new toxic metabolite was isolated from Penicillium paraherquei and the structure was determined by X-ray diffraction analysis. The metabolite was designated as paraherquamide. Paraherquamide(1), colorless prisms, mp244-247"(decomp.),[α]22 -28"(c=0.43, CH30H), C28H35N305(M+ m/e 493), UV λmax nm(ε): 226(32400), 260(6100), 290(1600); IR νmax cm-' : 3510, 3430, 3245, 1714, 1650; PMR δ in CDC13 : 0.86(3H,s), 1.10(3H,s), 1.45(6H,s), 1.65(3H,s), 1.85(lH,d,J=l5Hz), 1.77-2.40(5H,m), 2.55(lH,d,J=llHz), 2.58(lH,s,disappeared with D20), 2.67 (lH,d,J=l5Hz), 2.93-3.25(2H,m), 3.03(3H,s), 3.58(lH,d,J=llHz), 4.87(lH,d,J=8Hz), 6.30(lH,d,J=8Hz),6.64(lH,d,J=8Hz), 6.78(lH,d,J=8Hz), 8.33(lH,s,disappeared with D20). Dragendorf's test on 1 exhibited positive color. Catalytic hydrogenation of 1 over Pd-C gave a dihydro derivative(?), colorless needles, mp295-299"(decomp.). The signals of two methyl groups at 1.36 and 1.38ppm and of -CH2CH20- at 2.10(2H,d.d,J=4 and 6Hz) and 4.28(2H,d.d,J=4 and 6Hz)ppm were newly observed in the PMR spectrum of 1, instead, the signals of two methyls at 1.45 and of -CH2CH20- at 4.87 and 6.30ppm, which were observed in the spectrum of 1, disappeared. The presence of two carbonyl groups in 1 was indicated by appearance of the signals at 171.5 and 182.9ppm in the CMR spectrum. From the IR data, one of the carbonyl was shown forming the amide. On hydrolysis with 6N-HCl, 1 afforded some ninhydrine-positive products which were recognized on TLC-plate but none of them were identified with common amino acids. Paraherquamide(1) was crystallized from ethyl acetate to afford monoclinic, space group P2, with two molecules in a unit cell of dimensions; a=10.252(2), b=22.074(6), c=6.417(1) Å, β=99.95(3)°, Dx=1.14g/cm3. The intensity data were collected on a Rigaku automated four circle diffractometer with graphic monochromated CuKa radiation; 2538 independent reflections(|Fo|≥3σ(|Fo|) with 2θ≤140°) were observed. The structure was solved by RASA-IIF SAP system followed by multiple solution method 1) and Fourier synthesis. The block-diagonal least-square method, employed for the refinement of the positional and anisotropic temperature factors, reduced the R value to 0.079. All hydrogen atoms(34) except for OH were located by difference synthesis. The details of the toxicity of this compound will be reported elswhere. 2)