Preventive or therapeutic medicines for diabetes containing fused-heterocyclic compounds or their salts

A fused-heterocyclic compound of the formula (I′) or its salt:

• wherein G is CN, NO2, CO2R4
• wherein R4 is a hydrogen atom, an alkenyl group which may be substituted, an alkynyl group which may be substituted, a cycloalkyl group which may be substituted, a cycloalkenyl group which may be substituted, an aryl group which may be substituted or a heterocyclic group which may be substituted,
• SO2NRaRb
• wherein each of Ra and Rb which are independent of each other, is a hydrogen atom, a hydroxyl group, an alkoxy group, an alkyl group which may be substituted, an alkenyl group which may be substituted, an alkynyl group which may be substituted, a cycloalkyl group which may be substituted, a cycloalkenyl group which may be substituted, an aryl group which may be substituted or a heterocyclic group which may be substituted, or Ra and Rb together form a ring or
• CONRaRb, wherein Ra and Rb are as defined above;
• R1 is a halogen atom, a —O—R5 group
• wherein R5 is a hydrogen atom, an alkyl group which may be substituted, an alkenyl group which may be substituted, an alkynyl group which may be substituted, a cycloalkyl group which may be substituted, a cycloalkenyl group which may be substituted, an aryl group which may be substituted or a heterocyclic group which may be substituted,
• or a —S—R5 group wherein R5 is as defined above;
• R2 is a halogen atom, a —O—R5 group, wherein R5 as defined above, or an amino group which may be substituted;
• and
• each of R8 and R10 which are independent of each other, is a hydrogen atom, a halogen atom or an alkyl group;
• wherein the compound wherein G is CN, R1 is —SMe, R2 is NH2, R8 is Me, and R10 is hydrogen is excluded.