Intimal thickening inhibitory agent

A method for inhibiting proliferation of vascular smooth muscle cells, or for inhibiting thickening or vascular stenosis following percutaneous transluminal coronary angioplasty, comprising administering to a patient in need of said therapy an effective amount for said therapy of a compound of formula (1)

• wherein X is an oxygen atom;
• R1 is a hydrogen atom or an acyl group;
• R2 is a hydrogen atom, a lower alkyl group or a lower alkenyl group;
• R3 and R4 are taken together to form a 5-membered ring;
• R5 is a substituted or unsubstituted alkyl group having 1 carbon atom;
• and
• R6 is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted aryl group;
• provided that R6 is nil when R3 and R4 are taken together to form a benzofuran ring.