Compounds have formula (I), in which R , R may represent independently from each other hydrogen, lower alkyl, cycloalkyl or arylmethyl; R , R may represent independently from each other hydrogen, lower alkyl, or one of the groups -OR or -NR R , or they may form together with the atoms to which they are bound a five- to seven-membered carbocyclic ring or an heterocyclic ring containing one or two heteroatoms; R stands for lower alkenyl, cycloalkyl, cycloalkenyl, monocyclic arylalkyl, bicyclic aryl, biaryl or a group having formulae (a): R -X-alk- or (b), or forms together with R and the carbon atom to which it is bound a possibly substituted five- to seven-membered carbocyclic or heterocyclic ring; R stands for hydrogen, lower alkyl or arylmethyl; R , R represent independently from each other hydrogen or lower alkyl or form together with the nitrogen atom to which they are bound a five- or six-membered heterocyclic ring; R stands for hydrogen, lower alkyl, lower alkenyl, cycloalkyl, cycloalkenyl, mono- or bicyclic aryl, biaryl; R stands for a group having formula (a); X stands for a valence dash, oxygen or sulphur; Q stands for oxygen, sulphur or nitrogen; alk stands for a valence dash, a methylene chain, a saturated or unsaturated alkylene chain with 2-6 carbon atoms; n equals 0-3, m equals 0-2 and p equals 0-5. Also disclosed is a process for preparing said compounds and medicaments containing the same used for treating calcium metabolism disturbances.