New AChE inhibitors from microbial transformation of trachyloban-19-oic acid by Syncephalastrum racemosum

Abstract Trachyloban-19-oic acid ( 1 ) is a diterpene very abundant in nature and its structural modification can furnish new bioactive compounds. Biotransformation of 1 by fungus Syncephalastrum racemosum provided three derivatives, two hydroxylated products ( 2 – 3 ) and one product of rearrangement ( 4 ). Products 3 and 4 have never been reported so far, to the best of our knowledge. Structure of 3 was formed after oxidation and rearrangement of compound 2 . Compounds 1 – 4 were evaluated for inhibition of acetylcholinesterase, enzyme linked to the symptomatic control of Alzheimer’s disease. All the compounds presented inhibitory activity higher than starting material 1 , and product 3 presented IC 50  = 0.06 μM, which is about six times higher than activity found for galanthamine (IC 50  = 0.38 μM), the positive control used in this assay.