A new method for the preparation of nitrones through the aerobic oxidation of the corresponding N,N-disubstituted hydroxylamines has been developed by exploring a new catalytic reactivity of gold supported on silica. The oxidation occurs under very mild conditions (flux of air, methanol or water, room temperature). The oxidation of a range of highly functionalized hydroxylamines with complete conversions
Total Synthesis of (+)-Decarbamoylsaxitoxin and (+)-Gonyautoxin 3
作者:Osamu Iwamoto、Kazuo Nagasawa
DOI:10.1021/ol1006696
日期:2010.5.7
Facile construction of the complex saxitoxin (STX) skeleton is carried out by using a novel, conformationally controlled, guanidine cyclization process that relies on the use of neighboring group participation. The utility of this methodology is verified by its employment in syntheses of both natural and unnatural STX derivatives.
Total Synthesis of (−)- and (+)-Decarbamoyloxysaxitoxin and (+)-Saxitoxin
作者:Osamu Iwamoto、Ryoko Shinohara、Kazuo Nagasawa
DOI:10.1002/asia.200800382
日期:2009.2.2
AbstractPlaying the sax: The enantioselective total syntheses of (−)‐ and (+)‐decarbamoyloxysaxitoxin (doSTX) and (+)‐saxitoxin (STX) are reported. A new methodology was developed for the synthesis of STXs, featuring discriminative reduction of the nitro group and NO bond in nitroisoxazolidine.magnified imageEnantioselective total syntheses of (−)‐ and (+)‐decarbamoyloxysaxitoxin (doSTX) and (+)‐saxitoxin (STX) were achieved. The characteristic spiro‐fused cyclic guanidine structure of STX was constructed by oxidation at the C4 position with IBX via an α‐iminium carbonyl intermediate and acid‐promoted cyclization of guanidine at the C5 position. A second‐generation methodology was developed for the synthesis of STX, featuring discriminative reduction of the nitro group and NO bond in nitroisoxazolidine. This approach provides efficient access to the key diamine intermediate for STXs.
Synthesis of Skeletal Analogues of Saxitoxin Derivatives and Evaluation of Their Inhibitory Activity on Sodium Ion Channels Na<sub>V</sub>1.4 and Na<sub>V</sub>1.5
moderate inhibitoryactivity, were further evaluated by the use of the patch‐clamp method in cells that expressed NaV1.4 (a tetrodotoxin‐sensitive sodiumchannel subtype) and NaV1.5 (a tetrodotoxin‐resistant sodiumchannel subtype). These compounds showed moderate inhibitoryactivity towards NaV1.4, and weaker inhibitoryactivity towards NaV1.5. Uniquely, however, the inhibition of NaV1.5 by (−)‐FD‐dcSTX
合成具有融合型三环系统的沙毒素(STX)的骨架类似物,命名为FD-STX,作为候选钠离子通道调节剂。合成了三种在C13处具有不同取代度的FD‐STX衍生物4 a – c,并通过基于细胞的方法检测了它们对钠离子通道的抑制活性。( - ) - FD-STX(4)和( - ) - FD-dcSTX(图4b),其表现出中等的抑制活性,通过在电池中的使用膜片钳方法的所表达的Na进一步评价V 1.4(河豚毒素敏感的钠通道亚型)和Na V1.5(抗河豚毒素的钠通道亚型)。这些化合物对Na V 1.4表现出中等的抑制活性,而对Na V 1.5则表现出较弱的抑制活性。然而,独特的是,(-)-FD-dcSTX(4 b)对Na V 1.5的抑制是“不可逆的”。
Oxidation of <i>N</i>,<i>N</i>-Disubstituted Hydroxylamines to Nitrones with Hypervalent Iodine Reagents
Hypervalentiodine compounds are viable reagents for the oxidation of N,N-disubstitutedhydroxylamines to the corresponding nitrones, with IBX performing best. The procedure is very simple and user-friendly and affords the target compounds with high efficiency and regioselectivity, highlighting IBX as the reagent of choice for preparation of aldonitrones from nonsymmetric hydroxylamines. Evidence for