Effect of Cl substituent in the aromatic tetracycline ring on its reactivity with solvated electrons

Abstract

Decomposition yields of tetracycline hydrochloride /TC.HCl/ and chlorotetracycline hydrochloride /ClTC−HCl/ in methanol solution saturated with Ar or N₂O were determined. Rate constants of the reaction e_s with some antibiotics were obtained:

$$\begin{gathered} k/e_s^ - + ClTC \cdot HCl/ = 2 \cdot 49 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} ; \hfill \\ k/e_s^ - + TC \cdot HCl/ = 2 \cdot 86 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} \cdot \hfill \\ \end{gathered} $$

On the basis of the diffence between decomposition yields: ΔG=G₋TC.HCl^−G−ClTC.HCl′ 7-C−Cl group decomposition yield and the rate constant

$$k/e_s^ - + Cl - C - 7/ = 7 \cdot 94 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} $$

were determined. It was demonstrated by¹H NMR that the radical formed by degradation of 7-C−Cl group is recombined with the H atoms leading to ClTC.HCl being converted into tetracycline hydrochloride /TC.HCl/.