Two new naphthoquinones from the stem of Diospyros maritima
1Graduate Institute of Biotechnology, National Pingtung University of Science and Technology, Pingtung, Taiwan.
Journal of Asian Natural Products Research
|April 25, 2007
Abstract:
Two new naphthoquinones, 2-ethoxy-8'-hydroxyisodiospyrin (1) and 3-ethoxy-8'-hydroxyisodiospyrin (2), together with two known naphthoquinones, 6-hydroxy-5-methoxy-2-methyl-1,4-naphthoquinone and bisisodiospyrin were isolated from the stems of Diospyros maritima. The structures of 1 and 2 were established on the basis of spectroscopic data.
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Preparation of Diols and Pinacol Rearrangement
Compounds bearing two hydroxyl groups are known as diols. When the hydroxyl groups are located on adjacent carbon atoms, the diols are called vicinal diols or glycols. Under acidic conditions, vicinal diols undergo a specific reaction called pinacol rearrangement.
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
Oxidation of Phenols to Quinones
In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...


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