苯并唑类、2-氨基吲哚和环色胺类化合物的仿生合成研究
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摘要
苯并唑类、2-氨基吲哚和环色胺类氮杂环广泛存在于天然产物和有药用价值的化合物中。因此,通过有效的化学反应和途径来合成这类天然产物激起了人们广泛的研究兴趣。本论文主要研究这些氮杂环化合物的仿生合成,由以下两部分组成。第一部分主要介绍了在钯碳催化下,通过汉斯酯1,4-二氢吡啶这种仿生还原剂对邻取代硝基苯衍生物的还原,进而有效地合成了苯并嗯唑,苯并咪唑和吲哚类化合物。第二部分主要研究了在酸催化和氧化条件下色氨酸衍生物的偶联反应,以实现环色胺类生物碱的仿生合成。具体内容如下：
一、利用汉斯酯1,4-二氢吡啶这一辅酶NAD(P)H模型化合物为仿生还原剂,有效地实现了邻取代硝基苯类化合物还原环化反应。在钯碳的催化下,完成了硝基的还原和分子内环化的串联反应并生成了相应的苯并嗯唑、苯并咪唑和吲哚类化合物。在产氢实验和理论计算的基础上,我们推断汉斯酯-钯碳体系在还原邻取代硝基苯衍生物过程中有中间体钯氢产生。
二、在吲哚生物碱中,其中有一类化合物是以色氨的二聚、三聚甚至多聚形式存在于自然界中。这类天然产物主要是通过色胺或者色氨酸的3,3’位和3,7’位的偶联来构建的。我们通过对这类化合物生物合成途径的推测,认为这类化合物的合成可能是经历了色氨酸自由基或者色氨酸正离子的过程来实现的,其中季碳中心的立体构型可能是来源于色氨酸的手性诱导。我们尝试了不同的色氨酸衍生物在氧化或者酸催化下的反应。虽然没有得到希望的3,3’位和3,7’位偶联的产物,但是得到了一些其它重要的产物,比如色氨酸2,2’位和2,6’位偶联的产物。这为我们以后研究环色胺类生物碱的仿生合成奠定了基础。
Nitrogen heterocycles such as benzo-fused azoles,2-aminoindoles and cyclotryptamines are present in a variety of natural products and medicinally important compounds. Intrigued by efficient chemical reactions and elegant pathways for synthesis of the natural products in organism, this dissertation focuses on bioinspired synthesis of nitrogen heterocycles. The main body of the present dissertation consists of two parts. In the first part, benzoxazoles, benzimidazoles and indoles were efficiently synthesized by the reaction of ortho-substituted nitrobenzene derivatives with Hantzsch 1,4-dihydropyridine, a biomimetic reducing agent in the presence of catalytic Pd/C. In the second part, the coupling reactions of tryptophan derivatives in acidic or oxidative conditions were studied for biomimetic synthesis of cyclotryptamine alkaloids. The results are obtained as following:
1. Hantzsch 1,4-dihydropyridine, analogues of NAD(P)H, was develped as an efficient reducing agent in reductive cyclization of ortho-substituted nitrobenzene derivatives. In the presence of Pd/C as a catalyst, the tandem reduction and intramolecular cyclization gave corresponding benzoxazoles, benzimidazoles and indoles. On the basis of hydrogen evolution experiment and DFT calculations, we believe that the present reductive cyclization is very efficient and ortho-substituted nitrobenzene is reduced by palladium hydride generated from HEH in the presence of Pd/C.
2. The dimmers, trimers, and higher-order oligomers of tryptamine are the most abundant indoline alkaloids present in nature. The biological pathways for the synthesis of these cyclotryptamines may involve the 3,3'-coulpling or 3,7'-coulpling of tryptamines or tryptophans. We proposed that the free radicals or positive ions of tryptophan are the key intermediates existed in the biosynthesis and the stereoselectivities of reactions arise from tryptophan units. Therefore, a variety of tryptophan derivatives were tested in oxidative or acid-catalyzed conditions. Although the desired 3,3'-coulpling or 3,7'-coulpling products were not achieved, we obtained some important products such as 2,2'-coulpling and 2,6'-coulping products. The present work is fundamental to biomimetic synthesis of cyclotryptamines.
一、利用汉斯酯1,4-二氢吡啶这一辅酶NAD(P)H模型化合物为仿生还原剂,有效地实现了邻取代硝基苯类化合物还原环化反应。在钯碳的催化下,完成了硝基的还原和分子内环化的串联反应并生成了相应的苯并嗯唑、苯并咪唑和吲哚类化合物。在产氢实验和理论计算的基础上,我们推断汉斯酯-钯碳体系在还原邻取代硝基苯衍生物过程中有中间体钯氢产生。
二、在吲哚生物碱中,其中有一类化合物是以色氨的二聚、三聚甚至多聚形式存在于自然界中。这类天然产物主要是通过色胺或者色氨酸的3,3’位和3,7’位的偶联来构建的。我们通过对这类化合物生物合成途径的推测,认为这类化合物的合成可能是经历了色氨酸自由基或者色氨酸正离子的过程来实现的,其中季碳中心的立体构型可能是来源于色氨酸的手性诱导。我们尝试了不同的色氨酸衍生物在氧化或者酸催化下的反应。虽然没有得到希望的3,3’位和3,7’位偶联的产物,但是得到了一些其它重要的产物,比如色氨酸2,2’位和2,6’位偶联的产物。这为我们以后研究环色胺类生物碱的仿生合成奠定了基础。
Nitrogen heterocycles such as benzo-fused azoles,2-aminoindoles and cyclotryptamines are present in a variety of natural products and medicinally important compounds. Intrigued by efficient chemical reactions and elegant pathways for synthesis of the natural products in organism, this dissertation focuses on bioinspired synthesis of nitrogen heterocycles. The main body of the present dissertation consists of two parts. In the first part, benzoxazoles, benzimidazoles and indoles were efficiently synthesized by the reaction of ortho-substituted nitrobenzene derivatives with Hantzsch 1,4-dihydropyridine, a biomimetic reducing agent in the presence of catalytic Pd/C. In the second part, the coupling reactions of tryptophan derivatives in acidic or oxidative conditions were studied for biomimetic synthesis of cyclotryptamine alkaloids. The results are obtained as following:
1. Hantzsch 1,4-dihydropyridine, analogues of NAD(P)H, was develped as an efficient reducing agent in reductive cyclization of ortho-substituted nitrobenzene derivatives. In the presence of Pd/C as a catalyst, the tandem reduction and intramolecular cyclization gave corresponding benzoxazoles, benzimidazoles and indoles. On the basis of hydrogen evolution experiment and DFT calculations, we believe that the present reductive cyclization is very efficient and ortho-substituted nitrobenzene is reduced by palladium hydride generated from HEH in the presence of Pd/C.
2. The dimmers, trimers, and higher-order oligomers of tryptamine are the most abundant indoline alkaloids present in nature. The biological pathways for the synthesis of these cyclotryptamines may involve the 3,3'-coulpling or 3,7'-coulpling of tryptamines or tryptophans. We proposed that the free radicals or positive ions of tryptophan are the key intermediates existed in the biosynthesis and the stereoselectivities of reactions arise from tryptophan units. Therefore, a variety of tryptophan derivatives were tested in oxidative or acid-catalyzed conditions. Although the desired 3,3'-coulpling or 3,7'-coulpling products were not achieved, we obtained some important products such as 2,2'-coulpling and 2,6'-coulping products. The present work is fundamental to biomimetic synthesis of cyclotryptamines.
引文
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