A compound according to formula Ib: ** Formula ** in which X is O or S； R1 is H； or R1 is selected from C1-C6 alkyl, C3-C7 cycloalkyl, C3-C6 alkenyl, C3-C6 alkynyl and C1-C6 acyl； each of which may be optionally substituted with cyano, one or more halo, hydroxyl, or C1-C6 alkoxy； R2a is chosen from H, P (O) (OH) 2 and C (O) (CH2) n1C (O) OH； or R2a is selected from C1-C6 acyl and C3-C6 alkenyl； each of which may be optionally substituted with amino or carboxy； n1 is 0, 1, 2, 3 or 4； each R2b and R2c is independently selected from H and C1-C6 alkyl； oR2b and R2c can be joined to form a C3-C7 cycloalkyl； R3a is H, halo, cyano or nitro； each R3b is independently halo, cyano or nitro； each R4a and R4b is independently H, halo, cyano, carboxy or nitro； or each R4a and R4b is chosen from C1-C6 alkyl and C1-C6 alkoxy； each of which may be optionally substituted with one or more halo, or C1-C6 alkoxy； or R4a and R4b bind to form a 5 or 6 membered cycloalkyl, 5 or 6 membered heterocycloalkyl, 5 or 6 membered aryl or 5 or 6 membered heteroaryl； R4c is halo, cyano or nitro； and m1 is 0, 1 or 2； or pharmaceutically acceptable salts, and solvates of the compounds or solvates of their pharmaceutically acceptable salts.Un compuesto de acuerdo con la fórmula Ib:**Fórmula** en la que X es O o S； R1 es H； o R1 se elige entre C1-C6 alquilo, C3-C7 cicloalquilo, C3-C6 alquenilo, C3-C6 alquinilo y C1-C6 acilo； cada uno de los cuales puede estar opcionalmente sustituido con ciano, uno o más halo, hidroxilo, o C1-C6 alcoxi； R2a se elige entre H, P(O)(OH)2 y C(O)(CH2)n1C(O)OH； o R2a se elige entre C1-C6 acilo y C3-C6 alquenilo； cada uno de los cuales puede estar opcionalmente sustituido con amino o carboxi； n1 es 0, 1, 2, 3 o 4； cada R2b y R2c se elige independientemente entre H y C1-C6 alquilo； oR2b y R2c se pueden unir para formar un C3-C7 cicloalquilo； R3a es H, halo, ciano o nitro； cada R3b es independientemente halo, ciano o nitro； cada R4a y R4b es independientemente H, halo, ciano, c
