89

2013

26-31

Phytochemistry

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The C-26 amino group of steroidal alkaloids, such as tomatine, is introduced during an early step of their biosynthesis from cholesterol. In the present study, the mechanism of C-26 amination was reinvestigated by administering stable isotope labeled compounds, such as (26,26,26,27,27,27-2H6)cholesterol during biosynthesis of tomatine, solanine and solasonine. The chemical compositions of tomatine and solanine so obtained were analyzed by LC–MS after administering the d6-cholesterol to a tomato seedling and a potato shoot, respectively. The resulting spectra indicated that two deuterium atoms were eliminated from C-26 of cholesterol during biosynthesis. Furthermore, administration of (6-13C2H3)mevalonate in combination with lovastatin to an eggplant seedling, followed by GC–MS analysis of solasodine after TMS derivatization established that two deuterium atoms were eliminated from C-26 of cholesterol during solasonine biosynthesis. These findings are in contrast to an earlier observation that one hydrogen atom was lost from C-26 during tomatidine biosynthesis, and suggest that C-26 nitrogen atom addition involves an aldehyde intermediate. Thus, it is proposed that the C-26 amination reaction that occurs during steroidal alkaloid biosynthesis proceeds by way of a transamination mechanism.

EA 115

1397/11/10

Dashagha

117