Compounds are disclosed of general formula: ##STR1## wherein R.sup.1 is H, C.sub.1-6 alkyl or C.sub.3-6 alkenyl; R.sup.2 is H, C.sub.1-3 alkyl, C.sub.3-6 alkenyl, aryl, ar(C.sub.1-4)-alkylene, or C.sub.5-7 cycloalkyl;R.sup.3 is H or C.sub.1-3 alkyl;R.sup.4 and R.sup.5 each represents H, C.sub.1-3 alkyl or 2-propenyl, or R.sup.4 and R.sup.5 together form an aralkylidene group;R.sup.6 represents --CO.sub.2 R.sup.7, COR.sup.7, --COCO.sub.2 R.sup.7, or --CONHR.sup.7, whereR.sup.7 represents H, C.sub.1-4 alkyl, C.sub.3-7 cycloalkyl, C.sub.2-4 alkenyl, aryl or ar(C.sub.1-4)alkylene (with the provisos that (a) R.sup.7 does not represent H or benzyl when R.sup.6 is --CO.sub.2 R.sup.7 and (b) R.sup.7 does not represent alkenyl when R.sup.6 is --CONHR.sup.7); and Alk represents an alkylene chain containing two or three carbon atoms which may be unsubstituted or substituted by not more than two C.sub.1-3 alkyl group, and physiologically acceptable salts and solvates (e.g. hydrates) thereof.The compounds have potent and selective vasoconstrictor activity and are indicated as useful for the treatment of migraine. The compounds may be formulated as pharmaceutical compositions with physiologically acceptable carriers or excipients for administration by any convenient route. Various methods for the preparation of the compounds (I) are disclosed.