Rhyncholphylline; methyl (16Z)-16-(methoxymethylidene)-2-oxocorynoxan-17-oate; methyl (3xi,16E,20alpha)-16-(methoxymethylidene)-2-oxocorynoxan-17-oate; methyl (7beta,16E,20alpha)-16-(methoxymethylidene)-2-oxocorynoxan-17-oate; methyl (3xi,16Z,20alpha)-16-(methoxymethylidene)-2-oxocorynoxan-17-oate