Studies on the constituents of bulbs of the orchid prosthechea michuacana and antioxidant activity

Bioassay-guided fractionation of the chloroform extract of bulbs of the orchid P. michuacana was used to determine the chemical identity of bioactive constituents. The use of DPPH assay led to the isolation of two new lanostane triterpenoids 3α-acetoxy, 24-hydroxy-24-methyl-5α-lanosta-9(11),25- diene (1) and 3α-acetoxy, 24-hydroxy-24-methyl-5α-lanosta-9(11)ene (2), a new stilbene α-α'-dihydro,3',5',2-trimethoxy-3-hydroxy- 4-acetyl-4'-isopentenylstilbene (3), the phenanthrene 4,6,7-trihydroxy-2- methoxy-8-(methylbut-2- enyl)phenanthrene-1,1'-4',6',7'-trihydroxy-2'-methoxy- 8'-(methylbut-2'-enyl)phenanthrene (4), one new abietane-type diterpene 12-hydroxy-3β,7β,18α-triacetoxy-8,11,13-abietatriene (5), together with gigantol (6), a known compound. The compounds were identified by spectral analysis and comparison with spectroscopic data reported in the literature. Compounds 3, 4, 5, and 6 showed DPPH and ABTS radicalscavenging and anti-lipid peroxidation activities, but none of the isolated triterpenes showed promising antioxidant activity.