Soyasapogenol B (12-oleanene-3,22,24-triol) is a triterpene having an oleanane skeleton, which has been isolated from a soybean seed and determined for its structure (Chem. Pharm. Bull., 24, pp. 121-129, 1976, Chem. Pharm. Bull., 30, pp. 2294-2297, 1982) (Non-patent References 1 and 2), and its glycoside soyasaponin is broadly distributed in leguminous plants.
Regarding the soyasapogenol B, its anti-complement activity and platelet agglutination inhibitory action (JP-A-61-37749) (Patent Reference 1), antitumor activity (JP-A-10-234396) (Patent Reference 2) and hepatoprotective activity (Bioorg. Med. Chem. Lett., 7, 85-88, 1997) (Non-patent Reference 3) and the like have so far been reported, and its usefulness as a pharmaceutical preparation or a material thereof is expected.
Regarding the production method of soyasapogenol B, a method is known in which sugar chains of saponin contained in soybean seeds are hydrolyzed, and then soyasapogenol B is purified, but since the ratio of saponin contained in soybean seeds is about 0.2% which is very small (Yakugaku Zasshi (Journal of Pharmaceutical Sciences), 104, 162-168, 1984) (Non-patent Reference 4), more efficient production method is in demand.
It is considered that β-amyrin as a biosynthesis precursor of soyasapogenol B is biosynthesized by the ring-closure of 2,3-oxidosqualene which is formed via the mevalonate pathway, and soyasapogenol B is biosynthesized thereafter via two steps of hydroxylation reactions.
Sophoradiol (12-oleanene-3,22-diol) structurally close to soyasapogenol B is a substance which has been reported a component of Kaika(Sophora japonica) (Yakugaku Zasshi, 78, 1090-1094, 1958) (Non-patent Reference 5), and it is possible to produce soyasapogenol B by hydroxylation of the 24-position of sophoradiol.
Actually, a method for producing soyasapogenol B by hydroxylation of the 24-position of sophoradiol making use of a hydroxylase derived from a Glycyrrhiza glabra cultured cell has been disclosed (WO 02/086142) (Patent Reference 3).    Patent Reference 1: JP-A-61-37749    Patent Reference 2: JP-A-10-234396    Patent Reference 3: International Publication WO 02/086142    Non-patent Reference 1: Chem. Pharm. Bull., 24, pp. 121-129, 1976    Non-patent Reference 2: Chem. Pharm. Bull., 30, pp. 2294-2297, 1982    Non-patent Reference 3: Bioorg. Med. Chem. Lett., 7, 85-88, 1997    Non-patent Reference 4: Yakugaku Zasshi (Journal of Pharmaceutical Sciences), 104, 162-168, 1984    Non-patent Reference 5: Yakugaku Zasshi, 78, 1090-1094, 1958