(6b,8ξ,9ξ,12a,13a,14b,17b)-4-Ethyl-3,12-dihydroxy-4,10,14-trimethyl-17-[(2Z)-6-methyl-2,5-heptadien-2-yl]gonan-6-yl 2-O-(6-deoxy-a-L-mannopyranosyl)-b-D-glucopyranoside