Zanotti G, Petersen G, Wieland T
Department of Pharmaceutical Sciences, University La Sapienza, Rome, Italy.
Int J Pept Protein Res. 1992 Dec;40(6):551-8.
The amatoxins, highly toxic components of death cap Amanita mushrooms, bind strongly to RNA polymerase II (or B) in cell nuclei thus preventing the transcription of DNAs to hn-RNAs (Pre-mRNAs), the precursors of messenger RNAs. Three of the binding sites of the bicyclic octapeptides have been identified: an isoleucine side chain in position 6, a trans-4-hydroxyl group at proline in position 2 and a hydroxylated L-isoleucine side chain in position 3. No information exists about the stereochemical conditions at the beta-C-atom (C-atom 3) of this side chain. We have now synthesized the diastereomeric S-deoxo-amaninamides (Fig. 1) containing, in position 3, L-allo-isoleucine (analog 1), (2S, 3R)-2-amino-4-hydroxy-3-methyl butyric acid (analog 2), the diastereomer (2S, 3S)-2-amino-4-hydroxy-3-methylbutyric acid (analog 3) and D-isoleucine (analog 4). In the last synthesis, besides the "normal" bicyclic octapeptide 4, an isomeric Iso-4 was formed. The affinities for Drosophila RNA polymerase II were 100 times weaker as compared to gamma-amanitin for 1, 10 times weaker for 2, 200 times weaker for 3, 100 times weaker for 4, and more than 1000 times weaker for Iso-4. The results point to the importance of a methyl group in (R)-configuration at the beta-C atom of side chain 3.
鹅膏毒素是毒蝇伞蘑菇中的剧毒成分，它与细胞核中的RNA聚合酶II（或B）紧密结合，从而阻止DNA转录为信使RNA的前体——核不均一RNA（前体mRNA）。已确定双环八肽的三个结合位点：第6位的异亮氨酸侧链、第2位脯氨酸上的反式4-羟基以及第3位的羟基化L-异亮氨酸侧链。关于该侧链β-C原子（第3位碳原子）的立体化学条件尚无相关信息。我们现已合成了非对映体S-脱氧鹅膏酰胺（图1），其第3位含有L-别异亮氨酸（类似物1）、(2S, 3R)-2-氨基-4-羟基-3-甲基丁酸（类似物2）、非对映体(2S, 3S)-2-氨基-4-羟基-3-甲基丁酸（类似物3）和D-异亮氨酸（类似物4）。在最后一次合成中，除了“正常”的双环八肽4外，还形成了一种异构体Iso-4。与γ-鹅膏菌素相比，它们对果蝇RNA聚合酶II的亲和力，类似物1弱100倍，类似物2弱10倍，类似物3弱200倍，类似物4弱100倍，Iso-4弱1000倍以上。结果表明侧链3的β-C原子上具有(R)-构型的甲基很重要。
