La presente tiene una acción inhibidora selectiva de la PDE2A, el cual es útil como agente para la profilaxis o tratamiento de esquizofrenia, la enfermedad de Alzheimer y similar. Reivindicación 1: Un compuesto representado por la fórmula (1), caracterizado porque R¹ es un átomo de hidrógeno o un grupo alquilo C₁₋₆ opcionalmente sustituido; R² y R³ son cada uno de ellos independientemente un átomo de hidrógeno o un grupo alquilo C₁₋₆ opcionalmente sustituido, o R² y R³ en combinación forman opcionalmente, junto el átomo de carbono adyacente, un anillo opcionalmente sustituido; X es un enlace o un grupo alquileno C₁₋₆ opcionalmente sustituido; A es un grupo cíclico opcionalmente sustituido; Z¹ es un grupo representado por CRZ¹ en donde RZ¹ es un átomo de hidrógeno, un átomo de halógeno un grupo alquilo C₁₋₆ opcionalmente sustituido, un grupo alquenilo C₂₋₆ opcionalmente sustituido, un grupo alquinilo C₂₋₆ opcionalmente sustituido, un grupo alcoxi C₁₋₆ opcionalmente sustituido, un grupo amino opcionalmente sustituido, un grupo ciano o un grupo cíclico opcionalmente sustituido, o un átomo de nitrógeno; Z² es un grupo representado por CRZ² en donde RZ² es un átomo de hidrógeno, un átomo de halógeno un grupo alquilo C₁₋₆ opcionalmente sustituido, un grupo alquenilo C₂₋₆ opcionalmente sustituido, un grupo alquinilo C₂₋₆ opcionalmente sustituido, un grupo alcoxi C₁₋₆ opcionalmente sustituido, un grupo amino opcionalmente sustituido, un grupo ciano o un grupo cíclico opcionalmente sustituido, o un átomo de nitrógeno; Z³ es un grupo representado por CRZ³ en donde RZ³ es un átomo de hidrógeno, un átomo de halógeno un grupo alquilo C₁₋₆ opcionalmente sustituido, un grupo alquenilo C₂₋₆ opcionalmente sustituido, un grupo alquinilo C₂₋₆ opcionalmente sustituido, un grupo alcoxi C₁₋₆ opcionalmente sustituido, un grupo amino opcionalmente sustituido, un grupo ciano, un grupo alquilo C₁₋₆-carbonilo opcionalmente sustituido o un grupo cíclico opcionalmente sustituido, o un átomo de nitrógeno; y B es un heterociclo aromático que contiene nitrógeno que contiene 1 o 2 átomos de nitrógeno; siempre que 2,3-dihidro-1-metil-2-oxo-N-2-tiazolil-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-N-(4-metil-2-tiazolil)-2-oxo-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-2-oxo-N-(tetrahidro-2-oxo-3-furanil)-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-N-2-oxazolil-2-oxo-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-2-oxo-N-1H-1,2,4-triazol-3-il-6-[3-(trifluorometil)-fenil-1-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-2-oxo-N-4-piridinil-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)-carboxamida, 2,3-dihidro-1-metil-2-oxo-N-4-pirimidinil-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-2-oxo-N-5-pirimidinil-6-[3-(trifluorometil)-fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-2-oxo-N-3-piridazinil-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-N-[6-(4-morfolinil)-2-piridinil]-2-oxo-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, N-(4,5-dimetil-2-tiazolil)-2,3-dihidro-1-metil-2-oxo-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-N-(5-metil-2-tiazolil)-2-oxo-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, N-[5-[(dimetilamino)carbonil]-4-metil-tiazolil]-2,3-dihidro-1-metil-2-oxo-6-[3-(trifluorometil)-fenil]-pirido[2,3-b]pirazina-4-(1H)carboxamida, N-(4,6-dimetil-2-piridinil)-2,3-dihidro-1-metil-2-oxo-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-2-oxo-N-2-pirazinil-6-[3-(trifluorometil)fenil-1-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-2-oxo-N-2-pirazinil-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-2-oxo-N-2-pirimidinil-6-[3-(trifluorometil)fenil]-pirido[2,3-b]pirazin-4(H)carboxamida, N-[2-(1-azetidinil)-4-piridinil]-2,3-dihidro-1-metil-2-oxo-6-[3-(trifluorometil)fenil-1-pirido[2,3-b]pirazina-4(1H)carboxamida, 2,3-dihidro-1-metil-N-[6-(4-morfolinilmetil)-2-piridinil]-2-oxo-6-[3-(trifluorometil)-fenil-1-pirido[2,3-b]pirazina-4-(1H)-carboxamida, y N-[6-(1-azetidinil)-2-piridinil]-2,3-dihidro-1-metil-2-oxo-6-[3-(trifluorometil)-fenil]-pirido[2,3-b]pirazina-4(1H)carboxamida se excluyen; o una sal del mismo.The present has a selective inhibitory action of PDE2A, which is useful as an agent for the prophylaxis or treatment of schizophrenia, Alzheimer's disease and the like. Claim 1: A compound represented by the formula (1), characterized in that R¹ is a hydrogen atom or an optionally substituted C₁₋₆ alkyl group; R² and R³ are each independently a hydrogen atom or an optionally substituted C₁₋₆ alkyl group, or R² and R³ in combination optionally, together with the adjacent carbon atom, an optionally substituted ring; X is an optionally substituted C₁₋₆ alkylene group or bond; A is an optionally substituted cyclic group; Z¹ is a group represented by CRZ¹ wherein RZ¹ is a hydrogen atom, a halogen atom an optionally substituted C₁₋₆ alkyl group, an optionally substituted C₂₋₆ alkenyl group, an optionally substituted C₂₋₆ alkynyl group, an alkoxy group Optionally substituted C₁₋₆, an optionally substituted amino group, a cyano group or an optionally substituted cyclic group, or a nitrogen atom; Z² is a group represented by CRZ² where RZ² is a hydrogen atom, a halogen atom an optionally substituted C₁₋₆ alkyl group, an optionally substituted C₂₋₆ alkenyl group, an optionally substituted C₂₋₆ alkynyl group, an alkoxy group Optionally substituted C₁₋₆, an optionally substituted amino group, a cyano group or an optionally substituted cyclic group, or a nitrogen atom; Z³ is a group represented by CRZ³ wherein RZ³ is a hydrogen atom, a halogen atom an optionally substituted C₁₋₆ alkyl group, an optionally substituted C₂₋₆ alkenyl group, an optionally substituted C₂₋₆ alkynyl group, an alkoxy group Optionally substituted C₁₋₆, an optionally substituted amino group, a cyano group, an optionally substituted C₁₋₆-carbonyl alkyl group or an optionally substituted cyclic group, or a nitrogen atom; and B is a nitrogen-containing aromatic heterocycle containing 1 or 2 nitrogen atoms; provided that 2,3-dihydro-1-methyl-2-oxo-N-2-thiazolyl-6- [3- (trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazine-4 (1H) carboxamide, 2 , 3-dihydro-1-methyl-N- (4-methyl-2-thiazolyl) -2-oxo-6- [3- (trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazine-4 (1H) carboxamide, 2,3-dihydro-1-methyl-2-oxo-N- (tetrahydro-2-oxo-3-furanyl) -6- [3- (trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazine -4 (1H) carboxamide, 2,3-dihydro-1-methyl-N-2-oxazolyl-2-oxo-6- [3- (trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazine-4 ( 1H) carboxamide, 2,3-dihydro-1-methyl-2-oxo-N-1H-1,2,4-triazol-3-yl-6- [3- (trifluoromethyl) -phenyl-1-pyrido [2 , 3-b] pyrazine-4 (1 H) carboxamide, 2,3-dihydro-1-methyl-2-oxo-N-4-pyridinyl-6- [3- (trifluoromethyl) phenyl] -pyrido [2,3- b] pyrazine-4 (1 H) -carboxamide, 2,3-dihydro-1-methyl-2-oxo-N-4-pyrimidinyl-6- [3- (trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazine-4 (1H) carboxamide, 2,3-dihydro-1-methyl-2-oxo-N-5-pyrimidinyl-6- [3- (trifluoromethyl) -phenyl] -pyrido [2,3-b] pyrazine- 4 (1H) carboxamide, 2,3-dihydro-1-methyl-2-oxo-N-3-pyridazinyl-6- [3- (trifluoromethyl) phenyl] -pyrido [2,3-b ] pyrazine-4 (1H) carboxamide, 2,3-dihydro-1-methyl-N- [6- (4-morpholinyl) -2-pyridinyl] -2-oxo-6- [3- (trifluoromethyl) phenyl] - pyrido [2,3-b] pyrazine-4 (1 H) carboxamide, N- (4,5-dimethyl-2-thiazolyl) -2,3-dihydro-1-methyl-2-oxo-6- [3- ( trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazine-4 (1 H) carboxamide, 2,3-dihydro-1-methyl-N- (5-methyl-2-thiazolyl) -2-oxo-6- [ 3- (trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazine-4 (1 H) carboxamide, N- [5 - [(dimethylamino) carbonyl] -4-methyl-thiazolyl] -2,3-dihydro-1 -methyl-2-oxo-6- [3- (trifluoromethyl) -phenyl] -pyrido [2,3-b] pyrazine-4- (1 H) carboxamide, N- (4,6-dimethyl-2-pyridinyl) - 2,3-dihydro-1-methyl-2-oxo-6- [3- (trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazine-4 (1H) carboxamide, 2,3-dihydro-1-methyl -2-oxo-N-2-pyrazinyl-6- [3- (trifluoromethyl) phenyl-1-pyrido [2,3-b] pyrazine-4 (1H) carboxamide, 2,3-dihydro-1-methyl-2 -oxo-N-2-pyrazinyl-6- [3- (trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazine-4 (1H) carboxamide, 2,3-dihydro-1-methyl-2-oxo- N-2-pyrimidinyl-6- [3- (trifluoromethyl) phenyl] -pyrido [2,3-b] pyrazin-4 (H) carboxamide, N- [2- (1-azetidin il) -4-pyridinyl] -2,3-dihydro-1-methyl-2-oxo-6- [3- (trifluoromethyl) phenyl-1-pyrido [2,3-b] pyrazine-4 (1H) carboxamide, 2,3-dihydro-1-methyl-N- [6- (4-morpholinylmethyl) -2-pyridinyl] -2-oxo-6- [3- (trifluoromethyl) -phenyl-1-pyrido [2,3-b ] pyrazine-4- (1H) -carboxamide, and N- [6- (1-azetidinyl) -2-pyridinyl] -2,3-dihydro-1-methyl-2-oxo-6- [3- (trifluoromethyl) -phenyl] -pyrido [2,3-b] pyrazine-4 (1 H) carboxamide are excluded; or a salt thereof.