Amino acid spectra analysis compounds

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. 

The second major metabolite from T. inflation is structurally closely related to cyclosporin A, as can be deduced by elemental analysis, mass spectrum (m/z 1217), IR and NMR spectra. Furthermore, the presence of the double bond and OH group of the unusual MeBmt was established. Sulphonic acids in methanol or dioxane effected the typical rearrangement reaction by N, O-acyl migration to the iso-compound (13). Hydrolysis furnished the same amino acids as cyclosporin A with the exception of L-a-aminobutyric acid, which is replaced in cyclosporin C (12) by L-threonine. The amino-acid sequence could be deduced by conversion of cyclosporin C into cyclosporin A via the corresponding tosylate (14) and iodo derivatives (15) [7]. Position 2 for L-threonine as well as the assumed twisted -pleated sheet conformation of the molecule were confirmed by 13C-NMR spectra. 

Recent work, whereby the spectrum and concentrations of dissolved free amino acids were monitored by direct analysis of seawater from a fixed station over the period of a day at hourly intervals (K. Mopper, pers. comm., 1979), showed pronounced variations in both composition and concentration. Particularly striking was the sharp increase in basic amino acids (low C N) at the expense of a decrease in acidic-neutral acids (high C N) outside the daylight hours. An explanation can at present only be speculative, but the results suggest that the phenomenon is directly linked with photosynthetic activity. This suggests, therefore, that the approach to study excretion in situ requires the detection of bioactive compounds at their natural levels, which generaUy lie several orders of ms itude below those of bulk parfuneters. 

An interesting fact, first noticed by Wright (1937, 1939) is that the infrared spectrum of the DL-form of an amino acid is usually markedly different from the spectrum of either the d- or the L-form of the same acid when each is examined in the solid state. Wright attributes this to compound formation between the d- and L-forms. Darmon et al. (1948) have confirmed this observation, which is extremely important if infrared methods are to be used for the analysis of mixtures of amino acids, e.g., the estimation of leucine iso-leucine ratios in protein hydrolysates. In this connection, Gore and Petersen (1949) have reported differences between the spectra of L-threonine and D-threonine when examined in the solid state. They point out that this might arise from a polarization effect in the spectrometer. 

The data are typical for other amino-acid amides. The peak at 3370 cm- in the NH-stretching region of the compound studied corresponds to the indole VMH(r) stretching mode and the 3268 cm peak to a combination mode. All the obtained characteristic peaks for indole ring correlated well with the known ones for the pure amino acid tryptophan, and with theoretical vibrational analysis and IR spectroscopic data of some homo- and heterodipeptides with tryptophyl-fragments. The Raman spectrum of L-tryptophanamide esteramide ester amide of squaric acid diethyl ester is depicted in Figure 4.34. 

Mesoionic 4-amino-l,2,3,5-thiatriazoles constitute the only class of mesoionic 1,2,3,5-thiatriazoles known. They are prepared by the reaction of l-amino-l-methyl-3-phenylguanidine with approximately 2 equivalents of thionyl chloride with pyridine as solvent (88ACS(B)63>. They are obtained as the yellow 1 1 pyridine complexes (17). The dark-violet mesoionic 1,2,3,5-thiatriazole (18) was liberated on treatment with aqueous potassium carbonate (Scheme 3). The structure is established on the basis of elemental analysis and spectroscopic data. In particular, the IR spectrum is devoid of NH absorptions. Compound (18) exhibits a long-wavelength absorption at 463 nm in methanol. When mixed with an equivalent amount of pyridinium chloride, complex (17) is formed and the absorption shifts to 350 mn. The mesoionic thiatriazoles are sensitive towards mineral acids and aqueous base and although reaction takes place with 1,3-dipolarophiles such as dimethyl acetylene-dicarboxylate, a mixture of products were obtained which were not identified. 

---