prov:value
| - yl group, etc.The alkyl group represented by R.sub.6, R.sub.6 ' may be either straight, branched or cyclic, preferably one having 1 to 4 carbon atoms, such as ethyl, .beta.-sulfoethyl, etc.The heterocyclic group may include, for example, 2-(6-sulfo)benzthiazolyl group, 2-(6-sulfo)benzoxazolyl group and the like, which may also have a substituent such as a a halogen atom (e.g. fluorine atom, chlori
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