O-Methylation effect on the carbon-13 nuclear magnetic resonance signals of ortho-disubstituted phenols and its application to structure determination of new phthalides from Aspergillus silvaticus.
作者:MASAO FUJITA、MIKIKO YAMADA、SHOICHI NAKAJIMA、KENICHI KAWAI、MASAHIRO NAGAI
DOI:10.1248/cpb.32.2622
日期:——
The O-methylation effect on the carbon-13 nuclear magnetic resonance chemical shifts of ortho-disubstituted phenols was investigated. In phenols with nonconjugated ortho-disubstituents (1-10), O-methylation caused a downfield shift by an average of 5.2 ppm for the ortho-carbons (C-2 and -6), and a downfield shift by an average of 4.6 ppm for the para-carbon (C-4). These shift values are significantly different from those observed in ortho-monosubstituted and ortho-nonsubstituted phenols. This regularity is very useful for the spectral interpretation of some natural products with an ortho-disubstituted phenol group and for the determination of the position of the methoxy group in such compounds. Two new phthalides, silvaticol (15) and O-methylsilvaticol (16), were isolated along with nidulol (17) from Aspergillus silvaticus. In the course of the structure determination of these compounds, the O-methylation effects of ortho-mono-and ortho-disubstituted phenols were successfully applied to these phthalides. The structures of silvaticol and O-methylsilvaticol were determined as 6-hydroxy-4-methoxy-5-methylphthalide and 4, 6-dimethoxy-5-methylphthalide, respectively.
研究了 O-甲基化对正交二取代苯酚的碳-13 核磁共振化学位移的影响。在具有非共轭正交二取代基(1-10)的苯酚中,O-甲基化导致正交碳(C-2 和 -6)平均下移 5.2 ppm,对位碳(C-4)平均下移 4.6 ppm。这些移动值与在正一取代和正二取代苯酚中观察到的移动值明显不同。这种规律性对于解释某些具有正二取代酚基的天然产物的光谱以及确定甲氧基在此类化合物中的位置非常有用。从硅曲霉(Aspergillus silvaticus)中分离出了两种新的邻苯二甲酸酯,即硅烷醇(15)和 O-甲基硅烷醇(16)以及尼杜醇(17)。在确定这些化合物结构的过程中,成功地将正一取代酚和正二取代酚的 O-甲基化效应应用于这些邻苯二甲酸酯。硅烷醇和 O-甲基硅烷醇的结构分别被确定为 6-羟基-4-甲氧基-5-甲基邻苯二甲酸酯和 4,6-二甲氧基-5-甲基邻苯二甲酸酯。