✍ Scribed by Zhi-Jun Wu; Jian-Xin Pu; Li-Mei LI; Dong-Mei Fang; Hua-Yi Qi; Jian-Zhong Chen; Guo-You Li; Han-Dong Sun; Guo-Lin Zhang
No coin nor oath required. For personal study only.
Triterpenoids are a class of important natural product and are widely found in Chinese herb. Some of triterpenoids exhibit biological properties such as antiandrogenic, [1] antihepatitis B, [2] antitumor, [3,4] antioxidant, [5] anticomplement, [6] antimicrobial, [7] anti-HIV [8,9] and angiotensin converting enzyme-inhibitory activities. [10] The potential application brings the need for reliable, fast and low-cost analysis of this class of compounds.
Mass spectrometry (MS), especially tandem MS, has been one of the important physicochemical methods for the identification of trace natural products due to it rapidity, sensitivity, and low levels of sample consumption. [11 -14] Many triterpenoids have been rapidly analyzed using electrospray ionization (ESI)-MS or high-performance liquid chromatography (HPLC)-ESI-MS. [15 -18] In our laboratory, a series of triterpenoids possessing a unique skeleton, that is longipedlactone (Fig. 1), were isolated from the stems and leaves Kadsura longipedunculata. [9,19,20] Some of them showed significant cytotoxicity and anti-HIV activity. [9,19] The potential application prospect and unique skeleton prompted us to study the structural characterization of this series of compounds using MS. To our knowledge, these compounds have not been studied by electrospray tandem MS. To obtain sufficient information on the structure elucidation of this class of compounds, such as their degradation products, metabolites and biosynthesis intermediates, the detailed fragmentation patterns of longipedlactone triterpenoids were studied using ESI-quadrupole time-of-flight (QTOF) QTOF-MS/MS in both positive-and negative-ion modes.
HPLC-grade methanol was purchased from Fisher Scientific (Pittsburgh, PA). The deuteration of hydrogen on hydroxyl of compound 3 was carried out by incubation of 0.01-mg compound 3 in 2 ml CD 3 OD for 24 h. MS experiments were performed on a Bruker micrOTOF Q mass spectrometer in both positive-and negative-ion modes. Accurate masses of product ions were determined by external mass calibration using the mass calibrants of molecular weight (MW) 322.0481, 622.0290 and 922.0098 in the positive mode and of MW 431.9823, 601.9790 and 1033.9870 in the negative-ion mode. Helium gas was used as collision gas and high-purity nitrogen gas as nebulizer and dry gas at a pressure of 30 psi. The sample introduction rate was 115 µl/h. The ESI source conditions were as follows: Capillary V, -4500 V (positive), 4000 V (negative); End Plate voltage, -4000 V (positive), 3500 V (negative); Capillary Exit Voltage, 120 V; and the dry gas temperature, 150 • C. The Collision Energy was optimized to achieve sufficient fragmentation.
For the low-energy collision MS/MS analysis, the precursor sodiated molecular ions, [M+Na] + , were selected and the product ions were recorded by ESI-QTOF-MS/MS. Major fragmentation pathways of [M+Na] + at m/z 517 for longipedlactone F (1) are shown in Scheme 1(a) and (b). The accurate masses of product ions are shown in Table 1. A tandem McLafferty-type rearrangement plays a significant role in the skeleton fragmentation. The McLafferty-type rearrangement might involve evenelectron ions. [21,22] The product ion at m/z 365 (Fig. 2(a)) from m/z 517 was formed possibly by the fragmentation pathway. In the MS/MS spectrum of longipedlactone H (5) (Supporting Information) possessing the same structure of ring B as that of compound 1, the product ion at m/z 383 was generated from the precursor ion at m/z 535 likely by the tandem McLafferty-type rearrangement. A labeling experiment involving H/D exchange of compound 1 was carried out and corresponding MS/MS spectrum was shown in Fig. 2(b). The observation of product ion at m/z 365 from m/z 519 for deuterated longipedlactone F (1) indicated the rationality of proposed fragmentation mechanisms. Interestingly, the product ion at m/z 365 with high abundance was observed in the MS/MS spectrum of the precursor [M+Na] + at m/z 533 for longipedlactone G (3) (Fig. 3), although the structure of ring B is different from that of compounds 1 and 5. The process of forming the product ion at m/z 365 from the
📜 SIMILAR VOLUMES
Tetrodotoxin (TTX), a powerful sodium channel blocker, usually exists as a mixture of its analogs (TTXs) in natural sources. Due to the structural variation, some analogs are difficult to detect using the postcolumn liquid chromatography-fluorescent detection (LC-FLD) system. Liquid chromatography/e
## Abstract Diiodothyronines 3,5‐diiodothyronine (3,5‐T2), 3′,5′‐diiodothyronine (3′,5′‐T2), and 3,3′‐diiodothyronine (3,3′‐T2) are important metabolites of 3,5,3′‐triiodothyronine (T3) and 3,3′,5′‐triiodothyronine (rT3; reverse T3). In this paper, a novel and rapid method for identifying and quant
## Electrospray positive ionization tandem mass spectrometry of Amadori compounds The Maillard reaction, the nonenzymatic interaction between reducing sugars and amino acids, is one of the most important reactions in food and human bodies. 1,2 Amadori compounds are N-substituted 1-amino-1-deoxyket
## Abstract Porphyrin derivatives having a galactose or a bis(isopropylidene)galactose structural unit, linked by ester or ether bonds, were characterized by electrospray tandem mass spectrometry (ES‐MS/MS). The electrospray mass spectra of these glycoporphyrins show the corresponding [M + H]^+^ io