Establishing the metabolic network of isoquinoline alkaloids from the Macleaya genus Author Qing, Zhixing ** & * & Hunan Key Laboratory of Traditional Chinese Veterinary Medicine, Hunan Agricultural University, Changsha, 410128, China & School of Veterinary Medicine, Hunan Agricultural University, Changsha, 410128, China Author Yan, Fangqin Author Huang, Peng Author Zeng, Jianguo text Phytochemistry 2021 112696 2021-05-31 185 1 8 http://dx.doi.org/10.1016/j.phytochem.2021.112696 journal article 55397 10.1016/j.phytochem.2021.112696 26be6180-2c66-44fb-855c-9c0aa1377cce 1873-3700 8259854 2.3. Screening and identifying [ring- 13 C ]-labeled alkaloids from M. 6 cordata seedlings The [ ring - 13 C 6 ]-labeled isoquinoline alkaloids were screened from the TICs of M. cordata seedlings by EIC of the theoretical [ M +6.0201] + values ( M represents the m/z values of identified alkaloids). These labeled alkaloids were further identified by comparing their retention times, MS or MS / MS data with those of their unlabeled alkaloids. Take compound 2 as an example. An obvious peak was formed via EIC of m/z 320.1952 ([314.1751 + 6.0201] + ) on the TICs of M. cordata seedlings that were fed [ ring - 13 C 6 ]-tyrosine. In the MS spectrum of alkaloid 2 (Fig. S 5 A ), unlabeled ( m/z 314.1747) and labeled ( m/z 320.1952) mass-tocharge ratio values were observed. In the MS / MS spectrum of unlabeled m/z 314.1747 (Fig. S 5 B), the base peak ion at m/z 107.0483 was formed by β- cleavage of the skeleton. However, the corresponding fragment ion was found at m/z 113.0633 in the MS / MS spectrum of labeled m/z 320.1952, which indicated that the C-ring in the structure of alkaloid 2 was labeled (Fig. S 5 C ). In addition, the unlabeled ( m/z 175.0605) and labeled ( m/z 275.1370) fragment ions were also generated from the MS / MS spectrum of labeled parent ion, which further identified alkaloid 2 as demethylcolletine (Table S 2). When we used a similar method, a total of 120 [ ring - 13 C 6 ]-labeled isoquinoline alkaloids were screened and identified from the TICs of M. cordata seedlings (Table S 2). However, some of the identified isoquinoline alkaloids, such as compounds 52 and 193 , were not found to be labeled by [ ring - 13 C 6 ]. One reason is that the content of [ ring - 13 C 6 ]-isoquinoline alkaloids was low and hard to detect by HPLC-Q-TOF-MS. Another reason is that some unlabeled isoquinoline alkaloids, such as compounds 174 and 180 , were found from only M. microcarpa seedlings and not from M. cordata seedlings.