Department of Chemistry and Materials Science, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan.
Phytochemistry. 2013 May;89:26-31. doi: 10.1016/j.phytochem.2013.01.010. Epub 2013 Mar 6.
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-(2)H6)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-(13)C(2)H3)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.
甾体生物碱，如番茄碱的 C-26 氨基是在其生物合成过程中由胆固醇早期引入的。在本研究中，通过在番茄碱、龙葵碱和澳洲茄碱的生物合成过程中给予稳定同位素标记的化合物，如（26,26,26,27,27,27-(2)H6)胆固醇，重新研究了 C-26 氨化的机制。在分别向番茄幼苗和土豆芽中给予 d6-胆固醇后，通过 LC-MS 分析所得番茄碱和龙葵碱的化学组成。所得谱图表明，在生物合成过程中，胆固醇的 C-26 上消除了两个氘原子。此外，在向茄子幼苗给予（6-(13)C(2)H3)甲羟戊酸并结合 lovastatin 后，通过 TMS 衍生化后对澳洲茄碱进行 GC-MS 分析，确定在澳洲茄碱生物合成过程中，胆固醇的 C-26 上消除了两个氘原子。这些发现与早期观察到的番茄啶生物合成过程中 C-26 失去一个氢原子的观察结果相反，表明 C-26 氮原子的添加涉及醛中间体。因此，提出了甾体生物碱生物合成过程中发生的 C-26 氨化反应是通过转氨机制进行的。
