9H-pyrrolo-dipyridine derivatives

1. A compound of general formula I-A, or a pharmaceutically acceptable acid addition salt, a racemic mixture or its corresponding enantiomer and/or optical isomers thereof,

wherein

R1 is pyrazole, thiazole, pyridine, or pyrimidine each of which is optionally substituted by one or two substituents independently selected from (1) fluorine; (2) methyl, ethyl or propyl, each of which is optionally substituted by fluorine or methoxy; (3) cyano; (4) amino optionally substituted by methyl or fluoro-ethyl; (5) —C(O)NHR1A where R1A is methyl, ethyl, or propyl, each of which is optionally substituted by fluorine or methoxy; (6) methoxy, ethoxy or propoxy, each of which is optionally substituted by fluorine or methoxy; or (7) morpholine, piperazine or piperidine, each of which is optionally substituted by fluorine or fluoromethyl;

M is C—R3, and Q is CH; or M is CH, and Q is CR3;

R3 is (1) H; (2) fluorine; (3) methyl, ethyl or propyl, each of which is optionally substituted by fluorine, hydroxy or methoxy; (4) methoxy, ethoxy or propoxy, each of which is optionally substituted by fluorine, hydroxyl or methoxy; (4) di-methyl-amino; or (5) —NHR3A where R3A is methyl, ethyl or propyl, each of which is optionally substituted by fluorine, hydroxy or methoxy; and

wherein

any hydrogen of formula I-A is H, 2 H or 3 H;

any carbon of formula I-A is C, 14 C or 11 C; and

any fluorine of formula I-A is F or 18 F;

provided that the compound of formula I is not a compound of general formula Ro I

wherein

R is hydrogen or tritium;

F is fluoro or 18 fluoro;

or a pharmaceutically acceptable acid addition salt thereof.

2. A pharmaceutical composition comprising a compound according to claim 1 and a pharmaceutically acceptable excipient.

3. A method of diagnosing or monitoring tau aggregates in the brain of a subject, the method comprising administering a radiolabeled compound containing an isotope according to claim 1 to the subject.

4. A method of treating a subject with a neurodegenerative disease in which tau aggregates in the brain are implicated, the method comprising administering to the subject an effective amount of compound according to claim 1 .