This excerpt taken from the TPTX 10-Q filed Nov 9, 2006.
(6) Stockholder Rights Plan
We adopted a stockholder rights plan on May 16, 2005. The stockholder rights plan is designed to protect stockholders in realizing fair value and equal treatment in the event of an attempted takeover of the company and to protect us and our stockholders against coercive takeover tactics. The plan was not adopted as a result of any existing or proposed potential takeover threat.
Under the terms of the plan, we distributed one purchase right for each share of common stock outstanding to stockholders at the close of business on May 27, 2005. We will not issue a separate certificate for the rights unless and until they become exercisable.
Each right entitles the holder to purchase from us one one-thousandth of a share of a new series of participating preferred stock at an initial purchase price of $15. The rights will become exercisable and will detach from the common stock for a specified period after any person or group, without the approval of our board of directors, has become the beneficial owner of, or commences a tender offer or exchange offer for, 15% or more of the then outstanding shares of our common stock (subject to certain exceptions).