Compounds of formula I: wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, R.sup.9 and n are as defined in the description, processes for the preparing the compounds, new intermediates employed in the preparation, pharmaceutical compositions containing the compounds, and uses of the compounds in therapy.