<span class="citations"><p>Gian P. Vicario, Sergio Penco, Federico Arcamone, "Daunorubicin and doxorubicin labelled with .sup.14 C at the 14-position and processes for their preparation." U.S. Patent US4211864, issued March, 1976.</p>
</span><a href="https://www.google.com/?tbm=pts#q=4211864&amp;tbm=pts" rel="noopener" target="_blank">US4211864</a>