Abstract
Steviol glycosides were subjected to bacteria present in a soil sample collected from a Stevia plantation in Paraguay. During the incubation experiments, next to the aglycon steviol, steviol degradation products were also formed. X-ray analysis and NMR methods in combination with chemical synthesis and GIAO NMR calculations were used to fully characterize the structure of these compounds as a tricyclic ketone and the corresponding reduced form. They were nicknamed monicanone and monicanol. The latter has the (S)-configuration at the alcohol site.
Highlights
Steviol glycosides (SGs) are sweet substances isolated from the leaves of the shrub Stevia rebaudiana (Bertoni) Bertoni
Steviol glycosides were subjected to bacteria present in a soil sample collected from a Stevia plantation in Paraguay
The idea was that bacteria able to degrade SG would accumulate in soils that were repeatedly contacted with plant material containing these substances
Summary
Steviol glycosides (SGs) are sweet substances isolated from the leaves of the shrub Stevia rebaudiana (Bertoni) Bertoni. Repeated sub-cultivation of the bacterial population that developed from the soil sample in SMM (10% inoculum) at the moment of full conversion of the SGs to steviol furnished a stable bacterial community capable of converting SGs nearly quantitatively to steviol in one week. This consortium was routinely used for the bio-organic synthesis of steviol. Repeated resuspension of the bacterial suspension (0.1 L) in 0.9 L of SMM at the moment of attaining the maximum concentration of this new compound (eight times) led to the development of a new bacterial consortium that converted the SGs from SMM nearly quantitively to this new compound in twelve days.
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