1H-NMR-Spectrum of the 9 in D6-DMSO. The structure illustrates the shift calculation for protons of the compound with ChemDraw Ultra 2004. (Numbers indicate the predicted shift of the signals in ppm; quality of estimation is indicated in colour: blue = good, red = rough)
This open question for the synthesis of tetrazine-based dienes in aqueous solution is answered below. The possibility of the synthesis of tetrazines functionalized with aryl compounds is attractive and could be successful. As illustrated in schema/table 3 the synthesis worked via the following educts: 2-cyanopyrimidine 6 and 4-cyanobenzoic acid 7 react with 80% aqueous hydrazine 8 to the intermediate 3,6-diaryl-1,2-dihydro-1,2,4,5-tetrazine 9 in 40 to 50 % yield. The oxidation to the corresponding 1, 4-diaryl-1,2,4,5-tetrazine is next reaction step followed by the conversion to the acid chloride with thionyl dichloride which in turn was reacted with the Boc-mono-protected 1,3-propylenediamine to the propyleneamine substituted acid amide 10. After deprotection with TFA the amino group was transferred with the acid chloride derivative of the TMZ 11 to the TMZ-diaryl-tetrazine 12 a diene compound poised for the DARinv. The corresponding NMR H spectra are shown in the figures 2-5.
The Diels-Alder-Reaction with inverse-Electron-Demand, a very efficient versatile Click-Reaction Concept for proper Ligation of variable molecular Partners
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