The present invention relates to new acetylinic piperazine compounds of formula I, their pharmaceutically acceptable salts, and hydrates: wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, M, and n are as defined in the description. The invention also relates to processes for the preparation of the compounds and to new intermediates employed in the preparation, pharmaceutical compositions containing the compounds, and to the use of the compounds in therapy.