Two new cyclobutane-type lignans, named moslolignans A and B, together with two known ones, andamanicin and magnosalin, were isolated from the whole plant of Mosla scabra. Their structures were established as 1 beta*,2 beta*,3 alpha*,4 alpha*-l,2-dimethyl-3-(3- methoxy-4,5-methylene-dioxyphenyl)-4-(2,4,5-trimethoxyphenyl)-cyclobutane and 1 beta*,2 beta*,3 alpha*,4 alpha"-1,2-dimethyl-3-(2,5-dimethoxy-3,4-methylenedioxyphenyl)-4-(2,4, 5-trimethoxyphenyl)-cyclobutane by spectroscopic methods. This is the first report of naturally-occurring cyclobutane-type lignans with asymmetrical substitutions. (C) 2000 Elsevier Science Ltd. All rights reserved.