Acetic acid mass spectral peaks

The amino add analysis of all peptide chains on the resins indicated a ratio of Pro Val 6.6 6.0 (calcd. 6 6). The peptides were then cleaved from the resin with 30% HBr in acetic acid and chromatogra phed on sephadex LH-20 in 0.001 M HCl. 335 mg dodecapeptide was isolated. Hydrolysis followed by quantitative amino acid analysis gave a ratio of Pro Val - 6.0 5.6 (calcd. 6 6). Cycll2ation in DMF with Woodward s reagent K (see scheme below) yielded after purification 138 mg of needles of the desired cyc-lododecapeptide with one equiv of acetic add. The compound yielded a yellow adduct with potassium picrate, and here an analytically more acceptable ratio Pro Val of 1.03 1.00 (calcd. 1 1) was found. The mass spectrum contained a molecular ion peak. No other spectral measurements (lack of ORD, NMR) have been reported. For a thirty-six step synthesis in which each step may cause side-reaaions the characterization of the final product should, of course, be more elaborate. 

Figure 4b ESI mass spectral analysis of H-Thr-Arg-Asn-Leu-Ala-Asp-Gln-Glu-Asp-NH2. The spectrum was acquired on a Finnigan LCQ ion trap mass spectrometer the spectrum obtained by mathematical deconvolution is shown in the inset. The sample was dissolved at a concentration of approximately 0.5 pmol//xL in 50% acetonitrile containing 0.5% acetic acid and introduced into the mass spectrometer by direct infusion at a flow rate of 5 iL/min. Spectral averaging of 20 scans was employed. The small peaks in the spectrum were produced by in-source CAD of the peptide peaks such as these are frequently, but not always observed in ESI-MS analysis of small peptides.

Soviet chemists have examined (144) the pyrolyses of aconitine (4), benzoylacetyltalatizamine (205), diacetyltalatizamine (206), and 8-acetyl-14-ketotalatizamine (207) by mass spectral analyses at low (70-80°) and elevated (105-125°) temperatures. At temperatures above 100°, pyrolytic elimination of acetic acid occurred, while at 70-80° elimination was not observed. On the basis of observed steric interactions of the axial substituents at C-8, C-14, and C-16, they proposed that the relative ease of elimination of a C-8 acetate in these alkaloids is (4) = (205)>(206)> (207). Finally, they confirmed this postulate by observing the intensities of M+-AcOH and M+ — AcO peaks and their molecular ion peaks in the mass spectra of these alkaloids. 

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