<span class="citations"><p>Marino Gobetti, Guido Vandoni, "Acetylsalicylic acid thioesters, a process for their preparation and pharmaceutical compositions containing them." U.S. Patent US4563443, issued March, 1981.</p>
</span><a href="https://www.google.com/?tbm=pts#q=4563443&amp;tbm=pts" rel="noopener" target="_blank">US4563443</a>