The matrix-assisted molecular secondary ion mass spectra of viridopentaoses and their related compounds are discussed.
The effective use of matrices in molecular SIMS will be a powerful method for the structural characterization of polar molecules. Recently, sputtered type ionization methods such as plasma desorption(PD),2 laser desorption (LD),3 fast atom bombardment(FAB) 4 and secondary ion(S1) 5 mass spectrometry have been developed for the study of involatile and/or thermally labile compounds. These does not require heating of samples for desorption or ionization. In particular, molecular SIMS and FABMS have been worthy of notice because of their simple operation and good reproducibility. 6,7 The term FAB is used when the primary particles are neutral atoms instead of ions in SIMS. During the structural investigation of an antibiotic sporaviridin(SVD),S we obtained three heteropentasaccharides, viridopentaose AIlA), B(lB) and C(W) on hydrolysis of N-acetylsporaviridin(SVD-N-AC) with aqueous ammonia. Their structures have been established by chemical degradations and spectroscopic studies. 9 However, their molecular weights and sequence of the constituting units could be determined with difficulty by conventional methods such as chemical ionization(C1) and field desorption(FD) mass spectrometry. In this communication we describe the application of a new potential technique , matrix-assisted molecular SIMS to the structural characterization of viridopentaoses and their derivatives. Degradative reactions of @, 1B and 1C were performed as follows. 9 --Acidic methanolysis under appropriate conditions afforded viridotetraose A(3A), B(3B), C(3C) or viridotriose A(5A), B(5B), C(5C), respectively. Reduction with NaBH4 in MeOH yielded dihydroviridopentaose A(2A), B(2B) and C(2C), respectively. Treatment with 5% NaOH(aq) in MeOH eliminated readily an N-acetylacosamine to give unsaturated tetrasaccharides, G, 4B and s, respectively. -. Structural investigation of an antibiotic sporaviridin, part V. Part IV: see ref. 9.