Leonurine (1) is the uterotonic principle of Leonurus artemisia. We have developed a simple, high-yield synthetic procedure of 1 that is adaptable to large scale preparation. The synthesis involves the condensation of syringic acid and 4-guanidino-1-butanol hydrochloride in the presence of DDC using 1:1 HMPT-ether as solvent. The synthetic leonurine showed uterotonic activity in vivo and in vitro.
In a recent paper1 dealing with S , reactions of perhalogenobenzenes it was predicted that pentachlorofluorobenzene would be more reactive, replacing fluorine, than hexafluorobenzene, and this is now confirmed. Hammett substituent constants (a-) for pentachlorophenyl and pentafluorophenyl groups are derived and compared with values for ortho-and para-nitrophenyl groups.
Experimental MaterialsThe solvent and reagent were prepared as described.' 2,3,4,5,6-Pentachloro-I-fluorobenzene was prepared according to the procedure of Finger and Kruse2 from the commercially available pentachloronitrobenzene, using anhydrous potassium fluoride in dimethylformamide. The product, recrystallized from 95% ethanol, was obtained as long white needles of m.p. 137-138' (lit.2 137-138').
Kinetic ProcedureGenerally as described,' but runs were followed by estimating the concentration of reagent (0Me-) by potentiometric back-titration ~f excess quenching acid. A check by estimation of fluoride confirmed the reaction as simple replacement of F by 0Me. Good second-order plots were obtained, more precise by the acid-base method. Experimental kinetic data were measured over a range of about 30". Values of rate constants 103k2 (1. mole-I see-l) and temperature are: 3.30, 49.9'; 3.38, 50.1"; 5.53, 59.9"; 13.9, 65.1'; 21.6, 70.1"; 37.3 and 39.6, 80.1°. The Arrhenius parameters and other derived values are included in Table 1. The error in AEf computed by least squares is less than the estimated error in AEf of iO.5 kcal mole-'. Estimated error in logl,B is about i0.3.
ProductThe product, pentachloroanisole, was isolated from a reaction mixture allowed to proceed to "infinity", and was obtained as fine white needles, m.p. 108-109" (lit.3 108-110').
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