Synthesis of All Four Stereoisomers of (E)‐Vitamin KT (Phylloquinone), Analysis of Their Diastereoisomeric and Enantiomeric Purities and Determination of Their Biopotencies

Abstract

Abstract All four stereoisomers of ( E )‐vitamin Kb i. e. (2 1 E, 7 R, 11 1 R)‐l (= 1a), (2 1 E, 7 1 R, l1 1 S)‐1 (= 1b), (2 1 E, 7 1 S, 11 1 S) 1 ( = 1c), and (2 1 E, 7 1 S, 11 1 R)‐l ( = Id), have been synthesized in a state of high chemical and stereoisomeric purity. The synthesis of stereoisomers lb‐d relied on the use of the optically active Cf 1 * and C* 10 ‐building blocks ( R )‐ or ( S )‐4‐(benzyloxy)‐3‐methylbutanal (( R )‐ or ( S )‐2) and ( R )‐ or ( S )‐citronellal (( R )‐ or ( S )‐ 3 ) which had been secured by the Rh 1 ‐catalyzed allylamine‐to‐enamine isomerization technology. For the synthesis of the natural ( E )‐vitamin‐K1 stereoisomer 1a , a new route starting from natural phylol was developed, based on an O ‐alkylation/rearrangement procedure. A HPLC method was developed which separates with remarkable efficiency all four stereoisomers of (E) ‐ as well as three out of the four stereoisomers of ( Z )‐vitamin K 1 on optically active poly(trityl methacrylate) as the chiral stationary phase supported on Nucleosil. By this method, the stereoisomeric content of the stereoisomers 1b‐d synthesized was shown to be in the range of 96‐98 %, while the natural isomer 1a was configurationally uniform. The biological activity of the four ( E )‐vitamin‐K 1 stereoisomers was determined by means of the curative prothrombin time test with vitamin‐K‐depleted chicks. A high precision of the results was obtained with the recently introduced up‐and‐down organization of the test and the statistical evaluation according to an estimation procedure. With the natural ( E )‐vitamin‐K 1 stereoisomer 1a as standard (set at 1. 0), activities of 0. 93, 1. 19, and 0. 99 were found for stereoisomers 1b, 1c , and 1d , respectively. Within the confidence limits, these activity ratios can be regarded as identical, A very similar efficacy was obtained by comparison of ( E , all‐rac )‐vitamin K 1 ((2 1 E , RS , 11′ RS )‐ 1 ; equimolar mixture of the four stereoisomers 1a‐d) with the natural ( E )‐vitamin‐K 1 stereoisomer 1a ). A synergistic effect was not detectable, as was the case with the eight α‐tocopheryl‐acetate stereoisomers.