ubstituted amino group in which examples of the substituent thereof are an acyl or alkyl group (preferably those having 1 to 18 carbon atoms), etc.; a carbamoyl group; a sulfamoyl group; a carboxy group; an unsubstituted or substituted alkyl group which may be straight or branched chain (preferably, those having 1 to 30 carbon atoms; an unsubstituted or substituted aryl group (e.g., a phenyl group