金奮石斛醣類化學成分之研究

Abstract

金奮石斛 (Dendrobium Cassiope, 金童1號) 為金釵石斛 (Dendrobium nobile, ♀) 及奮起湖銅皮石斛 (D. moniliforme, ♂) 之雜交種，是一種蘭科石斛屬藥用植物，人工培養於臺灣。石斛是使用數千年的中草藥，具有多種生物活性，例如：抗糖尿病、預防心血管疾病、免疫調節等。石斛內含豐富的多醣類；然而，以層析法純化及分析多醣的方法相當地複雜及耗費時間，因此開發簡化的純化方法是必需的。本研究利用離心過濾法自金奮石斛水提取物中快速分離得到分子量大於3 kDa，介於3 kDa及1 kDa，以及小於1 kDa共三個部分。分子量3 kDa以上部分經由二乙胺基乙基纖維素管柱層析、核磁共振技術、單醣組成分析，主要成分DC-PS1為葡萄甘露聚醣(glucomannan)，甘露糖：葡萄糖之組成比例為100 : 12.5，並具有部分2-O及3-O乙醯基取代。其主幹為1,4鍵結的β-甘露糖和1,4鍵結的β-葡萄糖，另有1,6-α-甘露糖分支及β-甘露糖之終端糖基。經由高效分子篩層析及擴散排序核磁共振波譜分析其分子量為3.308 kDa，聚合度為20。分子量1 kDa至3 kDa部分則得到sucrose及shikimic acid，其中α-葡萄糖及β-果糖之比例為5 : 3。此部分不如預期得到寡醣成分，顯示離心過濾法對於分子量在1 kDa區間之分離效果不理想。

Dendrobium Cassiope (Taiseed Golden Boy No.1), a hybrid of Dendrobium nobile (♀) and D. moniliforme (♂), is a medicinal dendrobium (Shi Hu; Orchidaceae) cultivated in Taiwan. Dendrobium has been used as a traditional Chinese medicine for thousands of years. It shows several bioactivities, such as anti-hyperglycemic, beneficial for cardiovascular diseases, and immunity modulation. Dendrobium is abundant in polysaccharides (PS). Chromatographic purification and analyses of PS are complicated and time-consuming. Therefore, development of strategies with simplified procedures for PS are necessary. The present study utilized centrifugal filtration for rapid purification of the PS with different molecular weight (>3 kDa, 1 kDa-3kDa, and < 1 kDa) from the aqueous extract of Dendrobium Cassiope. The PSs with a molecular weight over 3 kDa and between 1 kDa to 3 kDa were purified by DEAE-cellulose column chromatography and characterized by nuclear magnetic resonance spectroscopy (NMR) and monosaccharides composition analysis. The purified PSs (DC-PS1) with a molecular weight over 3 kDa are acetyl glucomannans, with a backbone of β-(1→4)-mannose and β-(1→4)-glucose units in a ratio of 100:12.5, and with 1,6-α-mannose branches and β-mannose terminals. The molecular weight of purified PSs were estimated to be 3.308 kDa [a degree of polymerization (DP) of 20] by high performance size exclusion chromatography (HPSEC) and diffusion-ordered NMR (DOSY). The fraction with a molecular weight between 1 kDa to 3 kDa has sucrose and shikimic acid with α-glucose and β-fructose in a ratio of 5:3. The fraction does not contain oligosaccharides, thus the purifying efficacy of centrifugal filtration with molecular weight around 1 kDa is not favorable.