The present invention is directed to compounds of formula I: wherein X.sup.1, X.sup.2, X.sup.3, X.sup.4, X.sup.5, X.sup.6, X.sup.7, X.sup.8, X.sup.9, X.sup.10, R.sup.1, R.sup.2, R.sup.3, R.sup.4, and n are as defined for formula I 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.