摩熵化学
数据库官网
小程序
打开微信扫一扫
首页 分子通 化学资讯 化学百科 反应查询 关于我们
请输入关键词

黄酮类化合物

黄酮类化合物 定义与结构特征

黄酮类化合物是一大类天然存在的有机化合物,属于酚类衍生物。它们的分子结构通常包含两个苯环(A和B环)和一个三碳环(C环),形成一个基本骨架。该骨架由多个亚结构组成,包括黄烷醇、黄酮、黄酮醇等。

生物来源

黄酮类化合物广泛存在于植物界中,常见于许多蔬菜、水果及中药中。例如,在大豆、柑橘、茶叶和甘草中都可以找到它们的身影。

化学性质 亲水性与溶解度

由于其分子结构中含有多个酚羟基,因此具有一定的亲水性和良好的溶解性,这使得黄酮类化合物在药物设计中扮演重要角色。

稳定性与光敏性

大多数黄酮类化合物相对稳定,在适宜条件下不易发生降解。但某些类型的黄酮对光照比较敏感,容易被氧化,导致颜色变化。

生理活性与药用价值

黄酮类化合物因其丰富的生理活性而备受关注,主要包括:

  • 抗氧化作用:可有效清除体内自由基,保护细胞免受损伤。
  • 抗炎效应:有助于减轻炎症反应,缓解症状。
  • 心血管保护:可能通过多种机制改善心脑血管健康。
  • 抗癌潜力:研究表明某些黄酮类物质具有抑制肿瘤生长的能力。
应用领域 食品工业

作为一种天然色素和抗氧化剂,被广泛应用于食品加工中以提高其保质期及营养价值。

化妆品行业

利用其良好的生物相容性和抗衰老特性,在化妆品配方中应用广泛。

药物开发

由于黄酮类化合物展现出广泛的药理活性,已成为新药研发的重要候选目标之一。

中文名称 英文名称 CAS号 化学式 结构式图片
—— 2-amino-N,2-bis[6-[(2-phenyl-3,4-dihydro-2H-chromen-6-yl)oxy]pyridin-3-yl]-2-pyrrolidin-1-yl-N-(2-pyrrolidin-1-ylethyl)acetamide —— C52H54N6O5
2-amino-N,2-bis[6-[(2-phenyl-3,4-dihydro-2H-chromen-6-yl)oxy]pyridin-3-yl]-2-pyrrolidin-1-yl-N-(2-pyrrolidin-1-ylethyl)acetamide
—— 3,5-Dihydroxy-3',4'-dimethoxy-6,7-methylenedioxyflavone —— C18H14O8
3,5-Dihydroxy-3',4'-dimethoxy-6,7-methylenedioxyflavone
—— 2-[3-hydroxy-4-[(3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxyphenyl]chromen-4-one —— C21H20O9
2-[3-hydroxy-4-[(3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxyphenyl]chromen-4-one
—— 3,3-Diphenyl-8-(2-thiophen-2-ylethynyl)benzo[f]chromene;8-ethynyl-3,3-diphenylbenzo[f]chromene —— C58H38O2S
3,3-Diphenyl-8-(2-thiophen-2-ylethynyl)benzo[f]chromene;8-ethynyl-3,3-diphenylbenzo[f]chromene
—— [2-(3,4-dihydroxyphenyl)-5-[[2-(3,4-dihydroxyphenyl)-7-hydroxy-3-(3,4,5-trihydroxybenzoyl)oxy-3,4-dihydro-2H-chromen-5-yl]sulfanyl]-7-hydroxy-3,4-dihydro-2H-chromen-3-yl] 3,4,5-trihydroxybenzoate —— C44H34O18S
[2-(3,4-dihydroxyphenyl)-5-[[2-(3,4-dihydroxyphenyl)-7-hydroxy-3-(3,4,5-trihydroxybenzoyl)oxy-3,4-dihydro-2H-chromen-5-yl]sulfanyl]-7-hydroxy-3,4-dihydro-2H-chromen-3-yl] 3,4,5-trihydroxybenzoate
—— 3-[(2'R)-2-amino-2'-(3-methoxyphenyl)-3'-methyl-5-oxospiro[1H-imidazole-4,4'-2,3-dihydrochromene]-6'-yl]benzonitrile —— C26H22N4O3
3-[(2'R)-2-amino-2'-(3-methoxyphenyl)-3'-methyl-5-oxospiro[1H-imidazole-4,4'-2,3-dihydrochromene]-6'-yl]benzonitrile
—— (2S,3S,4S,5R)-6-[5-[(3R,4S,5S,6S)-6-carboxy-3,4,5-trihydroxyoxan-2-yl]oxy-2-(4-hydroxyphenyl)-4-oxochromen-7-yl]oxy-3,4,5-trihydroxyoxane-2-carboxylic acid —— C27H26O17
(2S,3S,4S,5R)-6-[5-[(3R,4S,5S,6S)-6-carboxy-3,4,5-trihydroxyoxan-2-yl]oxy-2-(4-hydroxyphenyl)-4-oxochromen-7-yl]oxy-3,4,5-trihydroxyoxane-2-carboxylic acid
—— [2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-3,4-dihydro-2H-chromen-3-yl] heptadecanoate —— C32H46O7
[2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-3,4-dihydro-2H-chromen-3-yl] heptadecanoate
—— (3S,4S,5S,6R)-2-[2-(3,4-dihydroxyphenyl)-5,7-dihydroxychromenylium-3-yl]oxy-6-(hydroxymethyl)-3-[(3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxane-3,4,5-triol —— C27H31O16+
(3S,4S,5S,6R)-2-[2-(3,4-dihydroxyphenyl)-5,7-dihydroxychromenylium-3-yl]oxy-6-(hydroxymethyl)-3-[(3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxane-3,4,5-triol
—— (7-Hydroxy-6-octadec-9-enoyl-3-octadec-9-enoyloxy-4-oxo-2-phenylchromen-5-yl) octadec-9-enoate —— C69H106O8
(7-Hydroxy-6-octadec-9-enoyl-3-octadec-9-enoyloxy-4-oxo-2-phenylchromen-5-yl) octadec-9-enoate
—— 2-[4-[(E)-7-hydroxy-3,7-dimethyloct-2-enyl]-1,3-benzodioxol-5-yl]-6-(3-hydroxy-3-methylbutyl)-5,7-dimethyl-2,3-dihydrochromen-4-one;methyl 2-bromoacetate —— C36H49BrO8
2-[4-[(E)-7-hydroxy-3,7-dimethyloct-2-enyl]-1,3-benzodioxol-5-yl]-6-(3-hydroxy-3-methylbutyl)-5,7-dimethyl-2,3-dihydrochromen-4-one;methyl 2-bromoacetate
—— [2-(3,4-Dihydroxyphenyl)-4-oxo-6,8-di(propanoyl)-3,7-di(propanoyloxy)chromen-5-yl] propanoate —— C30H30O12
[2-(3,4-Dihydroxyphenyl)-4-oxo-6,8-di(propanoyl)-3,7-di(propanoyloxy)chromen-5-yl] propanoate
—— 2-[1-[10-Methoxy-21,21-dimethyl-5-(4-morpholin-4-ylphenyl)-5-phenyl-6-oxapentacyclo[12.7.0.02,7.08,13.015,20]henicosa-1(14),2(7),3,8,10,12,15,17,19-nonaen-11-yl]piperidin-4-ylidene]pentanedioic acid —— C49H48N2O7
2-[1-[10-Methoxy-21,21-dimethyl-5-(4-morpholin-4-ylphenyl)-5-phenyl-6-oxapentacyclo[12.7.0.02,7.08,13.015,20]henicosa-1(14),2(7),3,8,10,12,15,17,19-nonaen-11-yl]piperidin-4-ylidene]pentanedioic acid
—— 1-[2-[4-(2-Fluoro-5,11-dihydrochromeno[4,3-c]chromen-11-yl)phenoxy]ethyl]piperidine —— C29H28FNO3
1-[2-[4-(2-Fluoro-5,11-dihydrochromeno[4,3-c]chromen-11-yl)phenoxy]ethyl]piperidine
—— 7-Chloro-2-(3-fluoro-4-nitrophenyl)chromen-4-one —— C15H7ClFNO4
7-Chloro-2-(3-fluoro-4-nitrophenyl)chromen-4-one
—— 1-[6-[(2-phenyl-3,4-dihydro-2H-chromen-6-yl)oxy]pyridin-3-yl]pyrrole-2,5-diol —— C24H20N2O4
1-[6-[(2-phenyl-3,4-dihydro-2H-chromen-6-yl)oxy]pyridin-3-yl]pyrrole-2,5-diol
—— 2-(3,4-Dihydroxyphenyl)-3-[3,4-dihydroxy-6-[(2,3,4-trihydroxy-5-methylcyclohexyl)oxymethyl]oxan-2-yl]oxy-5,7-dihydroxychromen-4-one —— C28H32O14
2-(3,4-Dihydroxyphenyl)-3-[3,4-dihydroxy-6-[(2,3,4-trihydroxy-5-methylcyclohexyl)oxymethyl]oxan-2-yl]oxy-5,7-dihydroxychromen-4-one
—— 2-phenyl-3-[(2S,3R,4R,5R,6S)-3,4,5-trihydroxy-6-methyloxan-2-yl]oxy-2,3-dihydrochromen-4-one —— C21H22O7
2-phenyl-3-[(2S,3R,4R,5R,6S)-3,4,5-trihydroxy-6-methyloxan-2-yl]oxy-2,3-dihydrochromen-4-one
—— (2S,3S,4S,5R,6S)-6-[5,7-dihydroxy-2-(4-hydroxyphenyl)-4-oxochromen-3-yl]peroxy-3,4,5-trihydroxyoxane-2-carboxylic acid —— C21H18O13
(2S,3S,4S,5R,6S)-6-[5,7-dihydroxy-2-(4-hydroxyphenyl)-4-oxochromen-3-yl]peroxy-3,4,5-trihydroxyoxane-2-carboxylic acid
—— 5-(5,7-dimethoxy-3,4-dihydro-2H-chromen-2-yl)benzene-1,2,3-triol —— C17H18O6
5-(5,7-dimethoxy-3,4-dihydro-2H-chromen-2-yl)benzene-1,2,3-triol
—— [2-(2,4-Dihydroxyphenyl)-5,7-dihydroxy-4-oxochromen-3-yl] 3,4,5-trihydroxybenzoate —— C22H14O11
[2-(2,4-Dihydroxyphenyl)-5,7-dihydroxy-4-oxochromen-3-yl] 3,4,5-trihydroxybenzoate
—— 2-(1,3-benzodioxol-5-yl)-4-(5-methylthiophen-2-yl)-6-propan-2-yloxy-2H-chromene-3-carboxylic acid;2-(1,3-benzodioxol-5-yl)-N-(4-propan-2-ylphenyl)sulfonyl-2-(2-propylphenoxy)acetamide;(5S,6R,7R)-7-[2-(2-carboxypropyl)-4-methoxyphenyl]-5-(2-fluoro-2-methyl-1,3-benzodioxol-5-yl)-2-(2-methylpropyl)-6,7-dihydro-5H-cyclopenta[b]pyridine-6-carboxylic acid —— C84H85FN2O19S2
2-(1,3-benzodioxol-5-yl)-4-(5-methylthiophen-2-yl)-6-propan-2-yloxy-2H-chromene-3-carboxylic acid;2-(1,3-benzodioxol-5-yl)-N-(4-propan-2-ylphenyl)sulfonyl-2-(2-propylphenoxy)acetamide;(5S,6R,7R)-7-[2-(2-carboxypropyl)-4-methoxyphenyl]-5-(2-fluoro-2-methyl-1,3-benzodioxol-5-yl)-2-(2-methylpropyl)-6,7-dihydro-5H-cyclopenta[b]pyridine-6-carboxylic acid
—— 2-(4-Fluorophenyl)-7-[[5-(2-methoxyphenyl)-1,2,4-oxadiazol-3-yl]methoxy]chromen-4-one —— C25H17FN2O5
2-(4-Fluorophenyl)-7-[[5-(2-methoxyphenyl)-1,2,4-oxadiazol-3-yl]methoxy]chromen-4-one
—— 8-methyl-2-(8-methyl-3,4-dihydro-2H-chromen-7-yl)-3,4-dihydro-2H-chromene —— C20H22O2
8-methyl-2-(8-methyl-3,4-dihydro-2H-chromen-7-yl)-3,4-dihydro-2H-chromene
—— 2-[1-[10-Methoxy-21,21-dimethyl-5-(4-morpholin-4-ylphenyl)-5-phenyl-6-oxapentacyclo[12.7.0.02,7.08,13.015,20]henicosa-1(14),2(7),3,8,10,12,15,17,19-nonaen-11-yl]-3-[3-[2-[2-[2-[2-[2-[2-(2-methylprop-2-enoyloxy)ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]-3-oxopropyl]piperidin-2-ylidene]acetic acid —— C65H76N2O14
2-[1-[10-Methoxy-21,21-dimethyl-5-(4-morpholin-4-ylphenyl)-5-phenyl-6-oxapentacyclo[12.7.0.02,7.08,13.015,20]henicosa-1(14),2(7),3,8,10,12,15,17,19-nonaen-11-yl]-3-[3-[2-[2-[2-[2-[2-[2-(2-methylprop-2-enoyloxy)ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]-3-oxopropyl]piperidin-2-ylidene]acetic acid
—— 2-[(2'R)-2-amino-3'-methyl-5-oxo-2'-phenylspiro[1H-imidazole-4,4'-2,3-dihydrochromene]-6'-yl]benzonitrile —— C25H20N4O2
2-[(2'R)-2-amino-3'-methyl-5-oxo-2'-phenylspiro[1H-imidazole-4,4'-2,3-dihydrochromene]-6'-yl]benzonitrile
—— 2-(3,4-Dihydroxyphenyl)-3-ethoxy-5,7-dihydroperoxy-6-hydroxychromen-4-one —— C17H14O10
2-(3,4-Dihydroxyphenyl)-3-ethoxy-5,7-dihydroperoxy-6-hydroxychromen-4-one
—— N-[5,7-dimethoxy-8-[2-methoxy-5-(1-nitrosoethyl)phenyl]-2-(4-methoxyphenyl)chromen-4-ylidene]hydroxylamine —— C27H26N2O7
N-[5,7-dimethoxy-8-[2-methoxy-5-(1-nitrosoethyl)phenyl]-2-(4-methoxyphenyl)chromen-4-ylidene]hydroxylamine
—— 7-[4,5-Dihydroxy-6-(hydroxymethyl)-3-oxooxan-2-yl]oxy-5-hydroxy-2-(4-methoxyphenyl)-8-(3-methylbut-2-enyl)-3-(3,4,5-trihydroxy-6-methyloxan-2-yl)oxychromen-4-one —— C33H38O15
7-[4,5-Dihydroxy-6-(hydroxymethyl)-3-oxooxan-2-yl]oxy-5-hydroxy-2-(4-methoxyphenyl)-8-(3-methylbut-2-enyl)-3-(3,4,5-trihydroxy-6-methyloxan-2-yl)oxychromen-4-one
—— 8-[3-(4-Oxochromen-2-yl)cyclohepta-1,3,6-trien-1-yl]-2-phenylchromen-4-one —— C31H20O4
8-[3-(4-Oxochromen-2-yl)cyclohepta-1,3,6-trien-1-yl]-2-phenylchromen-4-one
—— [5-(3,7-Dihydroxy-4-oxochromen-2-yl)-2-hydroxyphenyl]peroxy-pentan-3-ylphosphinic acid —— C20H21O9P
[5-(3,7-Dihydroxy-4-oxochromen-2-yl)-2-hydroxyphenyl]peroxy-pentan-3-ylphosphinic acid
—— 2-[[5,7-Dihydroxy-4-oxo-2-(2,3,4,5,6-pentamethylphenyl)chromen-3-yl]oxyamino]acetaldehyde;2-[[5,7-dihydroxy-4-oxo-2-(2,3,4,5,6-pentamethylphenyl)-2,3-dihydrochromen-3-yl]oxyamino]acetaldehyde —— C44H48N2O12
2-[[5,7-Dihydroxy-4-oxo-2-(2,3,4,5,6-pentamethylphenyl)chromen-3-yl]oxyamino]acetaldehyde;2-[[5,7-dihydroxy-4-oxo-2-(2,3,4,5,6-pentamethylphenyl)-2,3-dihydrochromen-3-yl]oxyamino]acetaldehyde
—— 5-Hydroxy-3,7-dimethoxy-2-[4-(3-methylbut-2-enoxy)phenyl]chromen-4-one —— C22H22O6
5-Hydroxy-3,7-dimethoxy-2-[4-(3-methylbut-2-enoxy)phenyl]chromen-4-one
—— 3,3-Diphenylbenzo[f]chromene-7,8,10-triol —— C25H18O4
3,3-Diphenylbenzo[f]chromene-7,8,10-triol
—— 2-(3,4-Dihydroxyphenyl)-3,5,7-trihydroxy-3,4-dihydrochromene-2-carbaldehyde —— C16H14O7
2-(3,4-Dihydroxyphenyl)-3,5,7-trihydroxy-3,4-dihydrochromene-2-carbaldehyde
—— N-(4-oxo-2-phenylchromen-7-yl)-2-[[5-[[4-(2-sulfanylacetyl)piperazin-1-yl]methyl]-1,3-benzodioxol-2-yl]sulfanyl]acetamide —— C31H29N3O6S2
N-(4-oxo-2-phenylchromen-7-yl)-2-[[5-[[4-(2-sulfanylacetyl)piperazin-1-yl]methyl]-1,3-benzodioxol-2-yl]sulfanyl]acetamide
—— 9a-phenyl-2H-furo[2,3-b]chromen-4-one —— C17H12O3
9a-phenyl-2H-furo[2,3-b]chromen-4-one
—— [2-(2-chlorophenyl)-5-hydroxy-8-[(3R)-3-hydroxy-1-methylpiperidin-4-yl]-4-oxochromen-7-yl] octadeca-9,12-dienyl carbonate —— C40H52ClNO7
[2-(2-chlorophenyl)-5-hydroxy-8-[(3R)-3-hydroxy-1-methylpiperidin-4-yl]-4-oxochromen-7-yl] octadeca-9,12-dienyl carbonate
—— 2-(3-Fluorophenyl)-7-[[5-[3-(trifluoromethyl)phenyl]-1,2,4-oxadiazol-3-yl]methoxy]chromen-4-one —— C25H14F4N2O4
2-(3-Fluorophenyl)-7-[[5-[3-(trifluoromethyl)phenyl]-1,2,4-oxadiazol-3-yl]methoxy]chromen-4-one
—— 3-[(2S,3R,4S,5S)-3,4-dihydroxy-5-(hydroxymethyl)oxolan-2-yl]oxy-2-(2,4-dihydroxyphenyl)-5,7-dihydroxychromen-4-one —— C20H18O11
3-[(2S,3R,4S,5S)-3,4-dihydroxy-5-(hydroxymethyl)oxolan-2-yl]oxy-2-(2,4-dihydroxyphenyl)-5,7-dihydroxychromen-4-one
—— [4-[7-[[5-(4-Fluorophenyl)-1,2,4-oxadiazol-3-yl]methoxy]-4-oxochromen-2-yl]phenyl]boronic acid —— C24H16BFN2O6
[4-[7-[[5-(4-Fluorophenyl)-1,2,4-oxadiazol-3-yl]methoxy]-4-oxochromen-2-yl]phenyl]boronic acid
—— [(3S,6S)-3,4,5-trihydroxy-6-[5-hydroxy-4-oxo-7-[(2S,3S,5S)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy-2-[4-[(2S,5S)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxyphenyl]chromen-3-yl]oxyoxan-2-yl]methyl 3-[4-[(2S,5S)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxyphenyl]prop-2-enoate —— C48H56O28
[(3S,6S)-3,4,5-trihydroxy-6-[5-hydroxy-4-oxo-7-[(2S,3S,5S)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy-2-[4-[(2S,5S)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxyphenyl]chromen-3-yl]oxyoxan-2-yl]methyl 3-[4-[(2S,5S)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxyphenyl]prop-2-enoate
—— (2S)-2-[3-(3,7-dimethylocta-2,6-dienyl)-4,5-dihydroxyphenyl]-5,7-dihydroxy-2,3-dihydrochromen-4-one —— C25H28O6
(2S)-2-[3-(3,7-dimethylocta-2,6-dienyl)-4,5-dihydroxyphenyl]-5,7-dihydroxy-2,3-dihydrochromen-4-one
—— (2R)-5,7-bis(phenylmethoxy)-2-(4-phenylmethoxyphenyl)-3,4-dihydro-2H-chromene —— C36H32O4
(2R)-5,7-bis(phenylmethoxy)-2-(4-phenylmethoxyphenyl)-3,4-dihydro-2H-chromene
—— 2-(3-Hydroxy-4-phenylmethoxyphenyl)-3,7-dimethylchromen-4-one —— C24H20O4
2-(3-Hydroxy-4-phenylmethoxyphenyl)-3,7-dimethylchromen-4-one
—— 5,7-Dihydroxy-3-(12-hydroxydodecyl)-2-(4-hydroxyphenyl)chromen-4-one —— C27H34O6
5,7-Dihydroxy-3-(12-hydroxydodecyl)-2-(4-hydroxyphenyl)chromen-4-one
—— 2-[2-[4-[2-(3-Chloro-4-methoxyphenyl)-3-methoxy-6-methyl-4-oxochromen-8-yl]piperidin-1-yl]ethyl]isoindole-1,3-dione —— C33H31ClN2O6
2-[2-[4-[2-(3-Chloro-4-methoxyphenyl)-3-methoxy-6-methyl-4-oxochromen-8-yl]piperidin-1-yl]ethyl]isoindole-1,3-dione
—— N-[[3-[8-(methanesulfonamido)-1-methoxy-6H-benzo[c]chromen-6-yl]phenyl]methyl]-4-methoxybenzenesulfonamide —— C29H28N2O7S2
N-[[3-[8-(methanesulfonamido)-1-methoxy-6H-benzo[c]chromen-6-yl]phenyl]methyl]-4-methoxybenzenesulfonamide
—— 5-Hydroxy-2-(3-hydroxy-4-phenylmethoxyphenyl)-7-methyl-3-phenylmethoxychromen-4-one —— C30H24O6
5-Hydroxy-2-(3-hydroxy-4-phenylmethoxyphenyl)-7-methyl-3-phenylmethoxychromen-4-one
—— 2-(1,3-benzodioxol-5-yl)-4-(5-methylthiophen-2-yl)-6-propan-2-yloxy-2H-chromene-3-carboxylic acid;2-(1,3-benzodioxol-5-yl)-N-(4-propan-2-ylphenyl)sulfonyl-2-(2-propylphenoxy)acetamide;(5S,6R,7R)-7-[2-(2-carboxypropyl)-4-methoxyphenyl]-5-(2-fluoro-2-methyl-1,3-benzodioxol-5-yl)-2-(propan-2-ylamino)-6,7-dihydro-5H-cyclopenta[b]pyridine-6-carboxylic acid —— C83H84FN3O19S2
2-(1,3-benzodioxol-5-yl)-4-(5-methylthiophen-2-yl)-6-propan-2-yloxy-2H-chromene-3-carboxylic acid;2-(1,3-benzodioxol-5-yl)-N-(4-propan-2-ylphenyl)sulfonyl-2-(2-propylphenoxy)acetamide;(5S,6R,7R)-7-[2-(2-carboxypropyl)-4-methoxyphenyl]-5-(2-fluoro-2-methyl-1,3-benzodioxol-5-yl)-2-(propan-2-ylamino)-6,7-dihydro-5H-cyclopenta[b]pyridine-6-carboxylic acid