Cyclobutanoid amides from Piper arborescens

Two new cyclobutanoid amides, piperarborenine A (= 1,1'-{[1alpha,2alpha,3beta,4beta)-2,4-bis(3,4-dimethoxyphenyl)cyclobutane-1,3-diylldicarbonyl)bis[5,6-dihydropyridin-2(1H)-one]; 1) and piperarborenine B (=1,1'{[(1alpha,2alpha,3beta,4beta)-2-(3,4-dimethoxyphenyl)-4-(3,4,5-trimethoxyphenyl)cyclobutane-1,3-diyl]dicarbonyl)bis[5,6-dihydropyridin-2(1H)-one]; 2) were isolated from the stem of Piper arborescens, besides two known cyclobutanoid amides, piperarboresine ( 1,1'-([(1alpha,2alpha,3beta,4beta)-2-(7-methoxy-1,3-benzodioxol-5-yl)-4-(3,4,5-trimethoxyphenyl)cyclobutane-1,3-diylldicarbonyl)bis[5,6-dihydropyridin-2(1H)-one]; 3) and piplartine-dimer A (= 1,1'-([(1alpha,2alpha,3beta,4beta)-2,4-bis(3,4,5-trimethoxyphenyl)cyclobutane-1,3-diyl]dicarbonyl}bis[5,6-dihydropyridin-2(1H)-one]; 4). The structures of the two new compounds were determined by spectral analyses.