Bolger M B, Wieland S, Hawkinson J E, Xia H, Upasani R, Lan N C
Department of Pharmaceutical Sciences, USC School of Pharmacy, Los Angeles 90033, USA.
Pharm Res. 1996 Oct;13(10):1488-94. doi: 10.1023/a:1016019327120.
Certain neuroactive pregnane steroids (also known as "epalons") are allosteric modulators of the GABA, receptor and have been shown to be potent anticonvulsants, anxiolytics, sedative/hypnotics, and anesthetic agents. The purpose of this study was to calculate the structural consequences of introduction of a double bond in the 16,17-position and to determine if this modification would selectively reduce sedative activity, but maintain the potent anticonvulsant activity of neuroactive steroids.
We have studied the biochemical and behavioral effects of introducing a 16,17 double bond into the naturally occurring neuroactive steroids, 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-P) and 3 alpha-hydroxy-5 beta-pregnan-20-one (3 alpha,5 beta-P) and three synthetic neuroactive steroid derivatives, 3 alpha-hydroxy-3 beta-methyl-5 alpha-pregnan-20-one (3 alpha,3 beta Me,5 alpha-P), 3 alpha-hydroxy-5 alpha-androstane (3 alpha, 5 alpha-A), and alphaxalone (3 alpha,5 alpha-11-one-P).
The 16-ene analogs of most of these neuroactive steroids were found to be 7- and 16-fold less potent in inhibiting [35S]TBPS binding to GABAA receptors and in a similar fashion, had reduced anticonvulsant and sedative potency in proportional amounts. The exception was the androstane (3 alpha,5 alpha-A) without a 17-acetyl group, that had virtually identical IC50 and ED50 values for the saturated and unsaturated derivatives. Calculation of the torsional energy profile for each of the 17-acetyl side chain conformations showed that the conformational energy minima found in the alpha,beta-unsaturated keto systems, produce an orientation of the 20-keto group that is rotated by 165 degrees when compared to the non-conjugated acetyl group (determined by X-ray crystallography and its minimum energy conformation).
The modified orientation of the 20-keto group of neuroactive steroids containing a 16-ene, provides an explanation for their decreased biological activity overall, but did not lead to an enhanced protective index.
某些具有神经活性的孕烷甾体（也称为“依帕隆”）是GABA受体的变构调节剂，已被证明是有效的抗惊厥药、抗焦虑药、镇静/催眠药和麻醉剂。本研究的目的是计算在16,17位引入双键的结构后果，并确定这种修饰是否会选择性降低镇静活性，但保持神经活性甾体的强效抗惊厥活性。
我们研究了在天然存在的神经活性甾体3α-羟基-5α-孕烷-20-酮（3α,5α-P）和3α-羟基-5β-孕烷-20-酮（3α,5β-P）以及三种合成神经活性甾体衍生物3α-羟基-3β-甲基-5α-孕烷-20-酮（3α,3βMe,5α-P）、3α-羟基-5α-雄甾烷（3α,5α-A）和alphaxalone（3α,5α-11-酮-P）中引入16,17双键的生化和行为效应。
发现这些神经活性甾体中的大多数16-烯类似物在抑制[35S]TBPS与GABAA受体结合方面的效力降低了7倍和16倍，并且以类似的方式，抗惊厥和镇静效力也相应降低。例外的是没有17-乙酰基的雄甾烷（3α,5α-A），其饱和和不饱和衍生物的IC50和ED50值几乎相同。对每个17-乙酰基侧链构象的扭转能分布进行计算表明，与非共轭乙酰基（通过X射线晶体学及其最低能量构象确定）相比，α,β-不饱和酮体系中发现的构象能最小值使20-酮基的取向旋转了165度。
含有16-烯的神经活性甾体20-酮基的修饰取向解释了它们整体生物活性降低的原因，但并未导致保护指数提高。
