Ozoe Y, Niina K, Matsumoto K, Ikeda I, Mochida K, Ogawa C, Matsuno A, Miki M, Yanagi K
Department of Life Science and Biotechnology, Shimane University, Matsue, Japan.
Bioorg Med Chem. 1998 Jan;6(1):73-83. doi: 10.1016/s0968-0896(97)00177-6.
Cyclic esters, S-esters, and amides of phenyl(thio)phosphonic acid were synthesized to probe the interaction between noncompetitive antagonists of ionotropic gamma-aminobutyric acid (GABA) receptors and their binding site. Some of these compounds competitively inhibited the specific binding of [3H]EBOB, a noncompetitive GABA antagonist, to rat-brain and housefly-head membranes. The trans isomer of the ester bearing a tert-butyl group at the 5-position and a bromine atom at the p-position (5t) was most potent in rat receptors with an IC50 value of 40 nM, while the trans isomer of the S-ester bearing the same substituents (10t) was most potent in housefly receptors with an IC50 value of 55 nM. In both cases, the corresponding amide analogue (12t) was less potent. The potencies of 5t and 12t tended to decrease in the presence of GABA, particularly in housefly receptors, while that of 10t remained unchanged. The rank order of activity in inhibiting [3H]EBOB binding to housefly-head membranes in the presence of GABA (10t > 5t > 12t) was in accord with that of insecticidal activity. S-Ester 10t depressed 10 microM and 300 microM GABA-induced 36Cl- influx into mouse cerebral synaptoneurosomes, whereas ester 5t depressed 10 microM GABA-induced 36Cl- influx but not 300 microM GABA-induced flux. Amide 12t was inactive at both GABA concentrations. These findings indicate that six-membered cyclic phenylthiophosphonic acid derivatives act as noncompetitive antagonists of GABA receptors and suggest that 10t is able to bind to the receptor in the open, desensitized, and closed states, whereas the affinity of 5t and 12t is lower in the open and desensitized states than in the closed state. The derivatives have similar structures except for the heteroatoms at the 1- and 3-positions, so that the heteroatoms may play a unique role when antagonists bring the open state of the GABA-gated channel to the desensitized or closed state.
合成了苯基（硫代）膦酸的环状酯、S-酯和酰胺，以探究离子型γ-氨基丁酸（GABA）受体的非竞争性拮抗剂与其结合位点之间的相互作用。其中一些化合物竞争性抑制了非竞争性GABA拮抗剂[3H]EBOB与大鼠脑和家蝇头部膜的特异性结合。在5位带有叔丁基且对位带有溴原子的酯的反式异构体（5t）在大鼠受体中活性最强，IC50值为40 nM，而带有相同取代基的S-酯的反式异构体（10t）在家蝇受体中活性最强，IC50值为55 nM。在这两种情况下，相应的酰胺类似物（12t）活性较低。在存在GABA的情况下，5t和12t的活性趋于降低，尤其是在家蝇受体中，而10t的活性保持不变。在存在GABA的情况下，抑制[3H]EBOB与家蝇头部膜结合的活性顺序（10t > 5t > 12t）与杀虫活性顺序一致。S-酯10t抑制了10 μM和300 μM GABA诱导的36Cl-流入小鼠脑突触神经小体，而酯5t抑制了10 μM GABA诱导的36Cl-流入，但不抑制300 μM GABA诱导的流入。酰胺12t在这两种GABA浓度下均无活性。这些发现表明，六元环状苯基硫代膦酸衍生物作为GABA受体的非竞争性拮抗剂，表明10t能够在开放、脱敏和关闭状态下与受体结合，而5t和12t在开放和脱敏状态下的亲和力低于关闭状态。这些衍生物除了1位和3位的杂原子外结构相似，因此当拮抗剂将GABA门控通道的开放状态转变为脱敏或关闭状态时，杂原子可能发挥独特作用。
