Prodrugs for systemic bioreductive activation-independent delivery of phyllohydroquinone, an active form of phylloquinone (Vitamin K-1) 1: Preparation and in vitro evaluation

With the aim of overcoming the delivery problems (water-solubility and bior eductive activation problems) of phyllohydroquinone (PKH), an active form o f phylloquinone (PK, vitamin K-1), the N,N-dimethylglycine esters of phyllo hydroquinone (I-mono, 1; I-mono, 2; and 1,4-bis, 3) have been synthesized a nd assessed in vitro as a prodrug for the systemic bioreductive activation- independent delivery of PKH. The hydrochloride salts of the esters were fou nd to be quite soluble in water. Hydrolysis of the esters in rat liver S9 f raction, rat plasma and phosphate buffer, pH 7.4, at 37 degrees C, was kine tically studied in the presence and absence of an esterase inhibitor. The h ydrolysis was catalyzed by esterases located in rat liver and rat plasma an d quantitatively yielded PKH, The enzymatic cleavage and the vitamin K-depe ndent carboxylation activity of the esters in the rat liver microsome prepa ration at pH 7.2 and 25 degrees C were studied. The regeneration of PKH fi- om the esters was catalyzed by carboxylesterases located in the rat liver m icrosome, and the order was as follows: 1>3>2, The carboxylation was stimul ated by selected ester 1 in the absence of dithiothreitol, an activator of the vitamin K cycle. The carboxylation activity of 1 was strongly inhibited in the presence of eserine, a carboxylesterase inhibitor. Compound I could also stimulate carboxylase under warfarin-poisoning conditions, where the vitamin K cycle was strongly inhibited. These results indicated that these highly water-soluble and Liver-esterase hydrolyzable ester derivatives of P KH are potential candidates for parenteral prodrugs which can thus achieve the systemic bioreductive activation-independent delivery of PKH.