Mass spectrometry of some N-acyldaunosamine derivatives.
Abstract The principal modes of fragmentation subsequent to electron impact of some N -acyl derivatives of daunosamine, the glycoside moiety of the antitumour antibiotics daunomycin and adriamycin, have been studied by using specifically deuterated derivatives and high-resolution measurements. In particular, the elimination of MeOH from methyl β-daunosaminides is shown to occur extensively and stereo-specifically, and involves HO-4. The splitting of the moieties C-1-C-2 and C-5-O-5 affords the fragments D 2 , D ′ 2 , and D ′′ 2 , which are among the most abundant.
A preparative synthesis of 3-amino-2,3,6-trideoxy-L-lyxo-hexose (daunosamine) hydrochloride from D-mannose.
A simple, preparative route in nine steps from methyl alpha-D-mannopyranoside (1) is described that affords, in 40% overall yield, the title amino sugar 11, the sugar constituent of the antitumor antibiotics adriamycin and daunorubicin. The 2,3:4,5-dibenzylidene acetal (2) of 1 is converted by butyllithium into the 2-deoxy-3-ketone 3, whose oxime 4 is reduced with high stereoselectivity to the D-ribo amine, isolated as its N-acetyl derivative 5 and converted by action of N-bromosuccinimide into the 4-O-benzoyl-6-bromide 7. Dehydrohalogenation of gives the 5,6-unsaturated glycoside 8, which, after O-debenzoylation to 9, undergoes stereospecific reduction by hydrogen with net C-5 inversion to give the crystalline, N-acetylated methyl beta-glycoside (10) of daunosamine, readily converted into daunosamine hydrochloride (11) and into the crystalline N-benzoyl (14) and N-acetyl(15) derivatives. No chromatographic procedures for isolation are required in any of the steps.
New method for analysis of enzymatic reactions: Thermolysin-catalyzed synthesis of aspartame precursor
Aspartame is an artificial sweetener which is 200 times sweeter than sucrose. A precursor of aspartame, N-(benzyloxycarbonyl)-l-aspartyl-l-phenylalanine methyl ester (Z-APM) was synthesized and hydrolyzed with thermolysin in an aqueous monophasic system. Graphical plotting methods and/or nonlinear regression have been used to analyze enzymatic reactions because of the nonlinearity of enzymatic rate equations. There are, however, problems: the former require accurate measurement of the initial reaction rate and the latter gives no analytical information. The authors proposed a method to solve the nonlinear enzymatic rate equations with respect to the concentration of a product with the Taylor expansion, especially for the reversible Theorell-Chance mechanism (Murakami, Y., Hirata, M., and Hirata, A., J. Ferment. Bioeng., 82, 246–252, 1996). This solution, however, is complex for practical use. In this paper, a simpler solution to explain the thermolysin-catalyzed synthesis of Z-APM is obtained. New methods to determine the kinetic parameters, especially for the reversible Theorell-Chance mechanism, based on the approximated solution are proposed. The results calculated using the obtained kinetic parameters can satisfactorily explain the experimental results, which demonstrates the effectiveness of the proposed analysis. We must know the relation between the concentrations of substrates and a product, and accurately evaluate of the result obtained using Taylor expansion when we determine the kinetic parameters using our newly developed methods. The methods to determine the kinetic parameters of the reversible Theorell-Chance mechanism described in this paper is, however, expected to be applied to general enzymatic reactions.