# Metabolite Profiling of _Christia__vevertilionis_ Leaf Metabolome via Molecular Network Approach
## 3 Results and Discussion
#### 3.1.1 Phenolic Acids
Since the MS/MS data of this compound (**15**) exhibited the same characteristic fragment ions as 7 at \(m/z\) 163, and 109, for [(caffeoyl+H)-H\({}_{2}\)O]\({}^{+}\), and 3,4-dihydroxyphenyl, respectively, it could be suggested that the additional isopropyl substituent (C\({}_{3}\)H\({}_{6}\), 42 Da) is directly attached to the carbon chain of the glycolic acid methyl ester moiety. In addition to the annotated spectral node via the GNPS library, which showed a precursor ion at \(m/z\) 344.134 [M + NH\({}_{4}\)]\({}^{+}\) for \(p\)-coumaric acid 4-\(O\)-glucoside (**17**), four other neighboring nodes, showing precursor ions [M + NH\({}_{4}\)]\({}^{+}\) at \(m/z\) 348.129, 318.119, 360.129, and 374.145, were also annotated as known phenolic acid glycoside molecules, namely, vanillic acid 4-\(O\)-glucose (**10**), \(p\)-hydroxybenzoic acid 4-\(O\)-glucose (**13**), caffeic acid 4-\(O\)-glucose (**14**), and ferulic acid 4-\(O\)-glucose (**22**), respectively. These compounds generated main characteristic fragment ions of their protonated aglycone molecules [(M+NH\({}_{4}\))-NH\({}_{3}\)-162]\({}^{+}\) at \(m/z\) 169 (**10**), 139 (**13**), 181 (14), 165 (**17**), and 195 (**22**), which originated from a direct cleavage of the \(O\)-glycosidic bond (glucose moiety, 162 Da) and the loss of ammonia. Further loss of one unit of their water molecule and/or successive loss of 46 Da (CO+H\({}_{2}\)O) from their protonated aglycone molecule were found consistent with the presence of carboxylic acid group within their parent structures. The fragmentation pathway proposed for compound **17** is provided in Figure S2 as a representative example for the common neutral losses observed in the fragmentation of phenolic acid glycoside molecules recorded in positive ion mode. Additionally, the presence of compounds **10**, **17**, and **22** can be further supported by the MS/MS data recorded in negative ion mode, as represented by the nodes at \(m/z\) 329.088 [M - H]\({}^{-}\), 325.093 [M - H]\({}^{-}\), and 355.103 [M - H]\({}^{-}\), respectively. These compounds showed the main fragment ion of their deprotonated aglycone molecules [(M - H)-162]\({}^{-}\) at \(m/z\) 167 (**10**), 163 (**17**), and 193 (**22**), resulting from a direct cleavage of the \(O\)-glycosidic bond. The spectral nodes assigned to Cluster M were classified as vanvilliic acid 4-\(O\)-glucose and a derivative of its structural isomer, which showed precursor ions [M - H]\({}^{-}\) at \(m/z\) 329.088 (**10**) and 397.075 (**6**), respectively. Compound **10** was characterized as vanillic acid 4-\(O\)-glucose, which produces a fragment ion at \(m/z\) 167 for [(M-H)-162]\({}^{-}\) due to direct cleavage at the \(O\)-glycosidic bond. Further decarboxylation and additional loss of proton gave rise to a fragment ion at \(m/z\) 122 for [(M-H)-162-COOH]\({}^{-\bullet}\), which was consistent with the MS/MS data reported by [PERSON] et al. [20]. With a mass difference of 68 Da (C\({}_{4}\)H\({}_{4}\)O) from that of **10**, along with the presence of identical fragment ions at \(m/z\) 329 and 122, the node with a precursor ion [M - H]\({}^{-}\) at \(m/z\) 397.075 (**6**) was initially proposed as a crotonylated derivative of **10**. However, the absence of a fragment ion at \(m/z\) 167 suggested that the parent structure of this compound was a phenolic acid ester, known as vanillic acid glucosyl ester, a structural isomer of **10** (Figure S3). Based on these MS/MS data, this compound was concluded to be a crotonylated derivative of vanillic acid glucosyl ester (**6**) that consisted of two feasible sites for the attachment of the crotonyl moiety (C\({}_{4}\)H\({}_{4}\)O), either at the hydroxyl group of C-4 or at one of the hydroxyl groups of the glucoside moiety. A detailed analysis of Cluster N revealed the compounds as dihydroxybenzoic acid derivatives. Through comparisons with literature data [20], the node with a precursor ion at \(m/z\) 401.072 [M \(-\) H]\({}^{-}\) was subsequently identified as dihydroxybenzoic acid malonyl hexoside (**16**).