Four new macrophyllin-type bicyclo[3.2.1]octanoid neolignans, (7S,8R,3′S,5′R)-Δ8′-5,5′,3′-trimethoxy-3,4-methylenedioxy-2′,3′,4′,5′-tetrahydro-2′,4′-dioxo-7.3′,8.5′-neolignan (cinerin A), 1, (7R,8R,3′S,4′R,5′R)-Δ8′-4′-hydroxy-5,5′-dimethoxy-3,4-methylenedioxy-2′,3′,4′,5′-tetrahydro-2′-oxo-7.3′,8.5′-neolignan (cinerin B), 2, (7S,8R,3′R,4′S,5′R)-Δ8′-4′-hydroxy-5,5′,3′-trimethoxy-3,4-methylenedioxy-2′,3′,4′,5′-tetrahydro-2′-oxo-7.3′,8.5′-neolignan (cinerin C), 3, and (7S,8R,2′R,3′S,5′R)-Δ8′-2′-hydroxy-5,5′-dimethoxy-3,4-methylenedioxy-2′,3′,4′,5′-tetrahydro-4′-oxo-7.3′,8.5′-neolignan (cinerin D), 4, along with the known diterpene kaurenoic acid 5, were isolated from the leaves of Pleurothyrium cinereum. The structures and configuration of these compounds were determined by extensive spectroscopic analysis. Cinerins A−D (1−4) were tested for their inhibition efficacy of platelet activating factor (PAF)-induced aggregation of rabbit platelets. Compound 3 was the most potent PAF antagonist. Compounds 1−5 were tested against Mycobacterium tuberculosis (H37Rv strain) using the MABA method. Compound 5 induced 91.3% growth inhibition at 50 μg mL−1. Compounds 1−5 showed no significant inhibitory activity against some Gram-positive and Gram-negative bacteria by the agar-well diffusion method.