A pyrrocidine derivative produced by fungus Neonectria ramulariae In-2 isolated from a Beetle Holotrichia picea

A new pyrrocidine A derivative, 19-epi-pyrrocidine A (1) was isolated from the insect–derived fungus Neonectria ramulariae In-2, together with known pyrrocidine A (2). The structure of 1 was determined by extensive 1D- and 2D-NMR, and MS spectral analyses. The absolute configuration of 2 was confirmed for the first time by X-ray crystallography. Compound 1 exhibited cytotoxicity against human acute promyelocytic leukemia HL60 cells (IC50 2.05 μM). In addition, semi-synthetic compounds 19-O-methyl-pyrrocidine A (3), 19-O-acetyl-pyrrocidine A (4), and 1,2-4,5-17,18-triepoxy-pyrrocidine A (5) were found to possess significant cytotoxicity, with IC50 values of 0.66 μM, 0.19 μM, and 2.00 μM, respectively.