| abstract |
A compound of the formula (I): <CHEM> Äwherein R<1> represents a C1-C6 alkyl group etc., R<2> and R<3> are the same or different and represent a hydrogen atom etc., R<a> represents a C1-C6 alkyl group etc., Arom represents an aryl group etc., A represents a C1-C6 alkylene group, E represents a single bond, an oxygen atom, a sulfur atom etc., X<1> and X<2> are the same or different and represent an oxygen atom or a sulfur atomÜ or a pharmacologically acceptable salt or ester thereof. |