Macleaya cordata, (Willd) R. Br. (Willd) R. Br.

Qing, Zhixing, Yan, Fangqin, Huang, Peng & Zeng, Jianguo, 2021, Establishing the metabolic network of isoquinoline alkaloids from the Macleaya genus, Phytochemistry (112696) 185, pp. 1-8 : 3

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. S5 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.S5 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.S5 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 S2). 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 S2). 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.