Pathways for the steroidal saponins conversion to diosgenin during acid hydrolysis of Dioscorea zingiberensis C. H. Wright

Diosgenin is an important starting material for the synthesis of steroidal hormone drugs in pharmaceutical industry. Acid hydrolysis of Dioscorea zingiberensis C. H. Wright (DZW) was the key step in the conversion of steroidal saponins to diosgenin in its manufacture factories. The pathways for the conversion of steroidal saponins to diosgenin during acid hydrolysis of DZW were studied experimentally. Three intermediate products and one byproduct were identified. The conversion pathways were from raw steroidal saponins zingiberensis newsaponin (1), deltonin (2), prosapogenin A of dioscin (3) to three intermediate products diosgenin-triglucoside (4), diosgenin-diglucoside (5) and trillin (6), and then to the product diosgenin (7) and byproduct 25-spirosta-3, 5-dienes (8). A maximum diosgenin yield of 2.5% was achieved when reacting in 0.8 M sulfuric acid for 6 h at 120 °C, while the intermediate products were just exhausted. After 6 h, the diosgenin yield decreased, due to the conversion of diosgenin to 25-spirosta-3, 5-dienes (8). The knowledge of the pathways for the conversion of steroidal saponins to diosgenin provide a scientific basis for assessing the performance of acid hydrolysis reaction in diosgenin manufacture factories by monitoring the content of three intermediate products (4–6). It also gives an alternative method for the synthesis of diosgenyl saponins (4–6) from plant material.

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► Diosgenin yield increased and then declined with time during acid hydrolysis of DZW.
► Pathways for steroidal saponins conversion to diosgenin were studied experimentally.
► Three intermediate products saponins (4), (5), (6) and byproduct (8) were identified.
► The decline of diosgenin yield was due to the conversion from diosgenin to (8).