Mass Spectra Analyses of Amides and Amide Dimers of Steviol, Isosteviol, and Steviolbioside

The mass spectra of a series of stevioside analogues including the amide and dimer compounds of steviol, isosteviol, and steviolbioside were examined. Positive ion mass spectral fragmentation of new steviol, isosteviol, and steviolbioside amides and the amide dimers are reported and discussed. The techniques included their synthesis procedures, fast-atom bombardment (FAB), and LC/MS/MS mass spectra. Intense [M+H]+ and [M+Na]+ ion peaks were observed on the FAB and ESI spectra. LC/MS/MS also yielded ES+ and ES？ ion peaks that fairly agreed with the results of the FAB and ESI studies. Mass spectral analysis of compounds 4p-q, 5a-g, 6, and 7 revealed the different cleavage pathway patterns that can help in identifying the structures of steviolbioside and its amide derivatives. 1. Introduction The mass spectrometry of these safe and sweet compounds such as steviol, isosteviol, and steviolbioside and their amides and amide dimer derivatives are an interesting current subject. Some reports [1] indicated that more than 50 of kaurane derivatives had been reviewed and presented in terms of specific activities which are antiparasitic, antimicrobial, antifertility, anti-inflammatory, and steroidogenesis. Bruno et al. [2] indicated the semisynthetic of ent-kauranes and the ester form displayed the antifeedant activity on insects. Compadre et al. [3] reported that the mass spectra analysis of this diterpenoid and its analogs revealed differences in stereochemistry, and Hussain et al. [4] used chemical ionization mass spectra to examine steviol and its aglycone. There were many reports to mention the toxicities [5], metabolism [6], bioactivities [7], microbial transformations [8], anti-HIV effects [9], genotoxicity [10], anti-inflammatory effects [11], and synthesis [12–14] of steviol, stevioside, isosteviol, and their derivatives dimers [15]. In this paper, we report our works on steviol derivatives, steviolbioside, and their synthetic compounds which were examined by a number of mass spectrometric techniques including electron impact (EI), fast atom bombardment (FAB), and electrospray with tandem mass spectrometry LC/MS/MS ESI. 2. Experimental For the synthetic purpose, steviol, isosteviol, and steviolbioside were prepared from stevioside, which was as obtained parts from plant extracts in China and purchased from Kyowa Foods Co. (Japan) as commercial food additives, via hydrolysis and purification by chromatography. The IR and NMR spectra were identified with those of the authentic sample [8, 12]. In the typical synthesis of amide reactions, alkylamines (1.1？eq)