The present invention provides compounds of formula (I) or pharmaceutically acceptable salts thereof: ##STR1## where A is C.sub.1-6 alkyl, C.sub.2-6 alkenyl, C.sub.2-6 alkynyl, C.sub.3-6 cycloalkyl, arylC.sub.1-6 alkyl, aryl, S(O),R.sup.1, OR.sup.1 or NR.sup.1 R.sup.6 ;R.sup.1 is hydrogen; C.sub.1-6 alkyl, C.sub.2-6 alkenyl, C.sub.2-6 alkynyl, C.sub.3-6 cycloalkyl or C.sub.3-6 cycloalkenyl each of which is optionally substituted by amino, C.sub.1-6 alkylamino, di(C.sub.1-6 alkyl)amino, C.sub.1-6 alkoxy, C.sub.1-6 alkylaminocarbonyl, one, two or three hydroxy groups, one, two or three halogen atoms or a four, five or six-membered saturated heterocyclic ring containing a nitrogen atom and optionally either an oxygen atom or a further nitrogen atom which ring is optionally substituted by C.sub.1-4 alkyl on the further nitrogen atom; aryl, arylC.sub.1-6 alkyl, arylC.sub.2-6 alkenyl or arylC.sub.2-6 alkynyl optionally substituted on the aryl ring by halogen, nitro, cyano, C.sub.1-6 alkylcarbonylamino, hydroxy or C.sub.1-6 alkoxy; or a five-membered aromatic ring containing 1, 2, 3 or 4 heteroatoms chosen from O, N and S provided that not more than one heteroatom is other than N, or a six-membered aromatic ring containing 1, 2, 3 or 4 nitrogen atoms, each of which rings is optionally substituted by halogen, C.sub.1-6 alkoxy, C.sub.1-6 alkylthio, aryl, C.sub.1-6 alkyl, C.sub.2-6 alkenyl or C.sub.2-6 alkynyl;R.sup.2 and R.sup.3 are independently hydrogen or C.sub.1-6 alkyl or together with the carbon atom to which they are attached form a C.sub.3-8 cycloalkyl group;R.sup.4 and R.sup.5 are individually hydrogen, C.sub.1-6 alkyl, C.sub.2-6 alkenyl, C.sub.2-6 alkynyl or C.sub.3-8 cycloalkyl or R.sup.12 and R.sup.13, together with the nitrogen atom to which they are attached, form a saturated 4 to 8 membered ring optionally containing an oxygen atom or a further nitrogen atom as a ring member, the further nitrogen atom being unsubstituted or substituted by C.sub.1-4 alkyl, C.sub.2-4 alkenyl or C.sub.2-4 alkynyl;R.sup.6 is hydrogen or C.sub.1-6 alkyl;p is zero, 1 or 2; andq is 0, 1 or 2;the preparation of these compounds, their use in enhancing cognition in disease states, particularly Alzheimer's disease, and methods of treatment using them.