The invention relates to compound of the formula I or a salt thereof, wherein the substituents are as defined in the specification； to its preparation, to its use as medicament and to medicaments comprising it.本發明係關於式I化合物：或其鹽，其中該等取代基如說明書中所定義；其製備；其作為藥劑之用途；以及包含其之藥劑。
