New acetylcholinesterase-inhibitory pregnane glycosides of Cynanchum atratum roots

Three new pregnane glycosides, cynatroside A (1), cynatroside B (2), and cynatroside C (3), isolated from the roots of Cynanchum atratum (Asclepiadaceae), were characterized as 7beta-{[O-alpha-L-cymaropyranosyl-(1 --> 4)-O-beta-D-digitoxopyranosyl-(l --> 4)-beta-D-oleandropyranosyl]oxy}-3,4,4a,4b,5,6.7,8,10,10a-decahydro-6alpha-hydroxy-4b-methyl-2-(2-methyl-3-furyl)phenanthren-1(2H)-one (1), 7beta-{[O-beta-D-cymaropyranosyl-(1-->4)-O-alpha-L-diginopyranosyl-(1-->4)-beta-D-cymaropyranosyl]oxy}-3,4,4a,4b,5,6,7,8,10,10a-decahydro-2,6alpha-dihydroxy-4b-methyl-2-(2-methyl-3-furyl)phenanthren-1(2H)-one (2), and 7beta-{[O-alpha-L-cymaropyranosyl-(1-->4)-O-beta-D-digitoxopyranosyl-(1-->4)-beta-L-cymaropyranosyl]oxy}-3,4,4a,4b,5,6,7,8,10,10a-decahydro-2,6alpha-dihydroxy-4b-methyl-2-(2-methyl-3-furyl)phenanthren-1(2H)-one (3), respectively. In addition, ten known constituents were identified, i.e., cynascyroside D (4), glaucoside C (5), glaucoside D (6), atratoside A (7), 2,4-dihydroxyacetophenone (8), 4-hydroxyacetophenone (9), syringic acid (10), azelaic acid (11), suberic acid (12), and succinic acid (13). Among these compounds, 1-4 significantly inhibit acetylcholinesterase activity.