<span class="citations"><p>Nicolae S. Bodor, Kenneth B. Sloan, Yu-Neng Kuo, "Method for synthesizing certain selected pro-drug forms of theophylline." U.S. Patent US4000132, issued January, 1956.</p>
</span><a href="https://www.google.com/?tbm=pts#q=4000132&amp;tbm=pts" rel="noopener" target="_blank">US4000132</a>