Mathiesen L, Malterud K E, Sund R B
Department of Pharmacology, School of Pharmacy, University of Oslo, Norway.
Free Radic Biol Med. 1997;22(1-2):307-11. doi: 10.1016/s0891-5849(96)00277-8.
A naturally occurring flavonoid, myrigalone B (2',6' -dihydroxy-4'-methoxy-3',5'-dimethyl-dihydrochal-cone) is an effective antioxidant and scavenger of the diphenylpicrylhydrazyl radical, while the closely related angoletin (2',4'-dihydroxy-6'-methoxy-3',5'-dimethyl-dihydrochalcone) is inactive. From NMR spectra, it appears that myrigalone B has a time-averaged conformation in which the substituted aromatic ring is orthogonal to the carbonyl group, while angoletin is coplanar. By donating a phenolic hydrogen in radical scavenging, myrigalone B will lose its symmetrical structure and may thereby change to a coplanar conformation forming a strong intramolecular hydrogen bond between the remaining phenolic hydrogen and the carbonyl group. The energy gain entailed would then appear to be a driving force for the radical scavenging by myrigalone B. Angoletin, being coplanar, lacks this driving force. To verify this hypothesis, the conformation and radical scavenging activity of a series of phenolic acetophenones were studied. All substances that had an orthogonal conformation and could form intramolecular hydrogen bonds by loss of a phenolic hydrogen were DPPH scavengers, while compounds lacking these properties were inactive. From this, we propose that formation of intramolecular hydrogen bonds may lead to radical scavenging activity.
天然存在的类黄酮化合物杨梅素B（2'，6'-二羟基-4'-甲氧基-3'，5'-二甲基二氢查耳酮）是一种有效的抗氧化剂和二苯基苦味酰基自由基清除剂，而与之密切相关的安哥拉亭（2'，4'-二羟基-6'-甲氧基-3'，5'-二甲基二氢查耳酮）则无活性。从核磁共振光谱来看，杨梅素B似乎具有一种时间平均构象，其中取代的芳环与羰基正交，而安哥拉亭是共平面的。在自由基清除过程中，杨梅素B通过提供一个酚羟基氢，会失去其对称结构，从而可能转变为共平面构象，在剩余的酚羟基氢和羰基之间形成一个强的分子内氢键。由此产生的能量增益似乎是杨梅素B进行自由基清除的驱动力。安哥拉亭由于是共平面的，缺乏这种驱动力。为了验证这一假设，研究了一系列酚乙酮的构象和自由基清除活性。所有具有正交构象且能通过失去一个酚羟基氢形成分子内氢键的物质都是二苯基苦味酰基自由基（DPPH）清除剂，而缺乏这些性质的化合物则无活性。据此，我们提出分子内氢键的形成可能导致自由基清除活性。
