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紫草素是从我国传统中药紫草中分离得到的一种脂溶性萘醌类化合物[1],是紫草的主要活性成分。研究表明紫草素具有抗肿瘤[2-4]、抗炎[5]、抗病毒[6]、抗菌[7]、促进伤口愈合[8]等药理作用。与其他萘醌类化合物类似,紫草素的稳定性较差,且在水中的溶解度低,这在一定程度上阻碍了紫草素的开发与应用[9]。
糖是自然界中存在最为广泛的生物分子,几乎存在于所有生命体中,通过糖苷化修饰可以提高化合物的水溶性和稳定性[10-11]。本课题组前期采用酶催化法已经制得两种紫草素吡喃葡萄糖苷,其稳定性均显著高于紫草素,水溶性相较紫草素增加上千倍,两种紫草素吡喃葡萄糖苷在体外抗肿瘤作用相较紫草素有所下降[12],但在后续开展的肝癌裸鼠移植瘤预实验中,紫草素-1′-O-β-D-吡喃葡萄糖苷的抑肿瘤作用明显优于紫草素。为了对其体内抗肿瘤作用进行全面研究,需要大量制备紫草素-1′-O-β-D-吡喃葡萄糖苷用于裸鼠移植瘤实验及药代动力学研究。但是在实验室条件下,通过酶催化法所得糖苷化合物的量只有微克级,难以满足动物实验的需要,而且酶的制备需要经过菌群培养、基因表达、构建重组质粒、提纯等多个步骤,这也导致了酶的制备成本高[13],因此迫切需要建立一种成本低、操作简便且适于大量制备紫草素-1′-O-β-D-吡喃葡萄糖苷的方法。
目前已有研究[14]采用三氯乙酰亚胺酯法将多种乙酰基取代的糖基加在紫草素1′-OH上,制得了11种紫草素苷,尚未见化学法合成紫草素-1′-O-β-D-吡喃葡萄糖苷的报道。本研究选择β-D-吡喃葡萄糖为起始原料,经选择性乙酰化后,再进一步制得糖基三氯乙酰亚胺酯作为糖苷供体,选择催化效能更佳的三氟甲磺酸三甲基硅脂来催化紫草素糖基化反应,制得紫草素-2, 3, 4, 6-四-O-乙酰基-β-D-吡喃葡萄糖苷,利用甲醇钠/甲醇醇解脱乙酰基后制得紫草素-1′-O-β-D-吡喃葡萄糖苷,并采用核磁共振法、质谱法对各产物的结构进行了鉴定。
三氯乙酰亚胺酯法合成紫草素-1'-O-β-D-吡喃葡萄糖苷
Synthesis of shikonin-1'-O-β-D-glucopyranoside by the trichloroacetimide ester method
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摘要:
目的采用三氯乙酰亚胺酯法合成紫草素-1'-O-β-D-吡喃葡萄糖苷。 方法以β-D-吡喃葡萄糖为起始原料制得糖基供体2,3,4,6-四-O-乙酰基-β-D-吡喃半乳糖酰基2,2,2-三氯乙酰亚胺酯,然后与紫草素反应得1-(1-(5,8-二羟基-1,4-萘醌-2-基)-4-甲基-3-戊烯氧基)-2,3,4,6-四-O-乙酰基-β-吡喃葡萄糖苷,最后在甲醇钠/甲醇体系下醇解脱去乙酰基得到目标化合物,采用核磁共振波谱(NMR)和电喷雾-质谱(ESI-MS)表征其结构。 结果NMR和ESI-MS鉴定目标化合物为紫草素-1'-O-β-D-吡喃葡萄糖苷。三氯乙酰亚胺酯法合成紫草素-1'-O-β-D-吡喃葡萄糖苷总收率为38.9%,HPLC测定纯度为96.7%。 结论本方法合成紫草素-1'-O-β-D-吡喃葡萄糖苷具有高立体选择性和高收率的优点,为紫草素糖基化修饰产物的化学合成提供了参考。 Abstract:ObjectiveTo synthesize shikonin-1'-O-β-D-glucopyranoside by the trichloroacetimide ester method. MethodsThe glycosyl donor 2, 3, 4, 6-tetra-O-acetyl-β-D-galactopyranoyl-2, 2, 2-trichloroacetyl was prepared from β-D-glucopyranose as starting material.The imine ester was then reacted with shikonin to obtain1-(1-(5, 8-dihydroxy-1, 4-naphthoquinone-2-yl)-4-methyl-3-pentenoxy)-2, 3, 4, 6-tetra-O-acetyl-β-glucopyranoside, and finally alcoholyzed to remove the acetyl group under the sodium methoxide/methanol system to obtain the target compound.The structure of the target compound was elucidated by nuclear magnetic resonance spectroscopy (NMR) and electrospray ionization mass spectrometry (ESI-MS). ResultsThe target compound was identified as shikonin-1'-O-β-D-glucopyranoside by NMR and ESI-MS.The total yield of shikonin-1'-O-β-D-glucopyranoside synthesized by the trichloroacetimide ester method was 38.9%, and the purity determined by HPLC was 96.7%. ConclusionsThe method has the advantages of high stereoselectivity and high yield.It can be used for the synthesis of shikonin-1'-O-β-D -glucopyranoside, and provide a reference for the chemical synthesis of shikonin glycosylation modified products. -
Key words:
- shikonin /
- glycosylation reaction /
- chemical synthesis
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