Functionalized dithia(2,5)pyridinophanes as vitamin B6 analogues. Synthesis, properties, and catalytic activity for racemization reaction.

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概要

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• Exploration of synthetic routes to achieve designed vitamin B<SUB>6</SUB> models on the structural basis of functionalized dithia(2,5)pyridinophanes from pyridoxine hydrochloride was undertaken and the catalyst potency for a racemization reaction was examined in comparison with that of pyridoxal. By the reaction of 3,4′-<I>O</I>-isopropylidenepyridoxine 2′,5′-dichloride with α,ω-dithiols, dithia(2,5)pyridinophanes were synthesized in good yields. For dithia[3]paracyclo[3](2,5)pyridinophanes, juncture sulfur atoms were extruded photochemically, whereas 2,(<I>n</I>+3)-dithia[<I>m</I>](2,5)pyridinophanes incompletely extruded sulfur atoms under various conditions. Because of instability and low preparative yield of 15-hydroxy-16-formyl[2]paracyclo[2](2,5)pyridinophane, dithia-containing phanes, (<I>n</I>+9)-hydroxy-(<I>n</I>+10)-formyl-2,(<I>n</I>+3)-dithia[<I>m</I>](2,5)pyridinophanes [<B>26a</B> (<I>n</I>=4), <B>26b</B> (<I>n</I>=6), <B>26c</B> (<I>n</I>=8); <I>m</I>=<I>n</I>+4], 17-hydroxy-18-formyl-2,11-dithia[3]paracyclo[3](2,5)pyridinophane (<B>27</B>), and an acyclic congener for <B>26a</B>, 5′-deoxy-2′,5′-bis(ethylthio)pyridoxal (<B>28</B>), were eventually prepared in high yields by use of manganese dioxide in the presence of a primary amine. It was found on the basis of <SUP>1</SUP>H-NMR spectral analyses that the rotations of pyridine rings in some molecules, <B>26a</B>, <B>26b</B>, and <B>27</B> with ring sizes equal to or less than fourteen were restricted. The racemization potency of <B>26a</B>–<B>c</B>, <B>27</B>, and <B>28</B> for sodium hydrogen L-glutamate demonstrated that these are 1.4- to 1.7-fold more potent than pyridoxal itself under certain conditions (pH 10.0, 25±0.5 °C) until <I>ca.</I> 80% completion of the racemization reaction. <B>26a</B> was found to be quite stable (no decomposition), but the others, <B>26b</B>, <B>26c</B>, and <B>28</B>, indicated 14, 8, and 12% decomposition, respectively. <B>27</B> was so unstable that a 63% decomposition was marked at the time of 56% completion of the racemization reacion.

• 公益社団法人 日本化学会の論文

著者

• Kuzuhara Hiroyoshi

  RIKEN (The Institure of Physical and Chemical Research)

• Iwata Masaaki

  RIKEN (The Institute of Physical and Chemical Research)

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