Abstract
Betulin (BE) has exceedingly become a potential natural product, providing multiple pharmacological and biological activities, including anti-cancer, anti-viral, and anti-inflammatory benefits. Previous research indicated that the solvatomorphism of BE can easily occur through crystallization with different organic solvents. This property of BE can directly affect its extraction, isolation, and preparation process. In this study, a system of thermogravimetry (TG)–differential thermal analysis (DTA) coupled with mass spectrometry (MS) with electron ionization (EI) and photoionization (PI) capability, equipped with the skimmer-type interface (i.e., skimmer-type interfaced TG–DTA–EI/PI–MS system), as a real-time and onsite analysis technique, was employed. Then, four solvatomorphs of BE, namely, with pyridine and water (A), sec-butanol (B), n,n-dimethylformamide (DMF) (C), and isopropanol (V), were analyzed for the first time. Finally, five kinds of the main volatile gaseous species, including H2O, pyridine, sec-butanol, DMF, and isopropanol, were identified clearly. Furthermore, the multi-step desolvation processes of the four solvatomorphs of BE were revealed by this system for the first time. This system showed great potential for the rapid and accurate analysis of various solvatomorphs of natural products.Graphic
Highlights
Betulin [BE, PubChem CID: 72326; lup-20 (29)-ene-3β, 28-diol], is a natural lupine-type pentacyclic triterpenoid, which is extracted and isolated mainly from the bark of birch trees (Betula spp., Betulaceae)
According to the TG results, all four solvatomorphs exhibited more than one weight loss-step in the range of 30–250 °C, suggesting that the desolvation process, as a characteristic thermal behavior of solvates, can be dispersed in sequence
For the solvatomorphs B, C, and V, the endothermic peaks caused by the desolvation process occurred in their differential thermal analysis (DTA) curves
Summary
Betulin [BE, PubChem CID: 72326; lup-20 (29)-ene-3β, 28-diol], is a natural lupine-type pentacyclic triterpenoid, which is extracted and isolated mainly from the bark of birch trees (Betula spp., Betulaceae). Certain natural products can form solvatomorphs with solvents in the extraction, isolation, or purification processes because of their inherent molecular structural properties. Solvatomorphs is regarded the only kind of crystalline form of natural products utilizable in single-crystal X-ray diffraction (SXRD) experiments, which is the most authoritative structural confirmation method besides total synthesis. As a pharmaceutical solid-state analytical technique, TG–MS analysis can obtain results that provide more abundant information about thermodynamic reaction processes than other characterization methods, such as powder X-ray diffraction, differential scanning calorimetry, Fourier transform infrared, and Raman spectroscopy, which are used to identify and characterize solvatomorphs. Four different solvatomorphs of BE and their singlecrystal structures were reported by Yang et al [8, 9] in a previous research Their thermodynamic reaction processes had not been studied further. The relationships between desolvation behavior and intermolecular interaction in the solvatomorphs of BE and the differences between EI and PI for analyzing solvatomorphs were revealed
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