【摘要】 本文系统地研究了土槿皮甲酸、乙酸和丙酸及其衍生物的质谱.通过质谱-结构关系的分析、高分辨质谱及亚稳数据的测定,阐明了它们在电子轰击下的裂解反应机制.更多还原

【Abstract】 A systematic study of the mass spectra of pseudolaric acid A（1A）, pseudolaric acid B（2A）, pseudolaric acid C（2B） and their derivatives （3A～9A, 1B, 3B～8B） has been undertaken in order to explore the fragmentation mechanisms of these compounds with novel carbon-skeleton.All these compounds revealed very weak molecular ion peaks （or none at all in most cases） as a result of the great lability to loss neutral fragments under electron impact. Two distinctively different degradation patterns were found depending on the substituent present at the bridge-head position C（4）.The mass spectral reactions of the 4-OAc series were initiated by the fission of C （3）-C（11） bond, leading to the ion series at m/z 260 （a₂）, 242（a₄）, 224（a₅）, 214 （a₆） （Scheme 1） and m/z 147 or 177+14n（b₁）, 131 （b₂） （Scheme 2）, respectively. The preferential cleavage of ring B （M⁺→m/z 214 and subsequentions） was proved by incorporating p-BrC₆H₄COCH₂ moiety to the carboxyl terminal of the side chain as an indicative isotopic label. Completely different behaviors were observed in the 4-OH series （β-hydroxylactones）, where the initial reaction was triggered predominantly by C（3）-C（4） bond cleavage followed by loss of H₂O, CO₂, R²OH or HCO₂ R² to give the ions c₁～c₄ （Scheme 3）. Either 4-OH or 4-OAc substituted diterpene acids gave m/z 110+R²（d₁） and 111 （d₂） through eyclization elimination （Scheme 4）.The mechanisms of fragmentation so far postulated were substantiated by high resolution data and metastable measurement.更多还原