Stereochemical variations on the colchicine motif. Part 2.1 Unexpected tetracyclic isoxazole derivatives
作者:Ulf Berg、Håkan Bladh、Maria Hoff、Christer Svensson
DOI:10.1039/a701400g
日期:——
Attempts to expand the colchicine B-ring in
7-oxodeacetamidothiocolchicine 1 by a Beckmann-type rearrangement lead
to unexpected tetracyclic isoxazole derivatives 2 and 3. The syntheses,
crystal and solution structures, conformational interconversions and
binding properties to tubulin are reported. The molecules exist as
mixtures of two enantiomeric conformations due to hindered rotation
around the A and C rings, which are twisted by dihedral angles of
62° (1) and 46° (2) in the crystal. Solid, solution and gas
phase (according to MM2) structures are compared. Dynamic 1H
NMR analyses give the following thermodynamic parameters for the
rotation around the A–C pivot bond: (1)
ωG‡381K
= 77.4; (2)
ωG‡300K
= 60.7;
ωH‡ =
55.6 ± 1.6 kJ mol-1;
ωS‡ =
-16.7 ± 15 J mol-1
K-1; (3)
ωG‡298K
= 60.1,
ωH‡ =
59.9 ± 2.0 J mol-1 and
ωS‡ =
-0.7 ± 15 J mol-1
K-1. The drugs 1 and 2 depolymerize microtubules by
binding to tubulin according to both in vitro and in vivo
studies, but 1 is considerably more active than 2. Compound 3 does
not seem to bind notably to tubulin.
尝试通过贝克曼式重排来扩展 7-oxodeacetamidothiocolchicine 1 中的秋水仙碱 B 环,结果产生了意想不到的四环异噁唑衍生物 2 和 3。报告了这些衍生物的合成、晶体和溶液结构、构象互变以及与小管蛋白的结合特性。由于围绕 A 环和 C 环的旋转受阻,这些分子以两种对映体构象的混合物形式存在,它们在晶体中的二面角分别为 62°(1)和 46°(2)。对固体、溶液和气相(根据 MM2)结构进行了比较。动态 1H NMR 分析得出了围绕 A-C 枢键旋转的热力学参数:(1) ωG‡381K = 77.4;(2) ωG‡300K = 60.7;ωH‡ = 55.6 ± 1.6 kJ mol-1;ωS‡ = -16.7 ± 15 J mol-1 K-1;(3) ωG‡298K = 60.1,ωH‡ = 59.9 ± 2.0 J mol-1,ωS‡ = -0.7 ± 15 J mol-1 K-1。根据体外和体内研究,1 号和 2 号药物通过与微管蛋白结合来解聚微管,但 1 号的活性比 2 号高得多。化合物 3 与微管蛋白的结合似乎并不明显。