**Except as otherwise indicated in footnote (1), the shares
were sold in multiple transactions at prices within the price range indicated.
(1) The shares were sold in multiple transactions at a single
price of $94.30 per share.
In addition to the transactions set forth
in the table above:
|·||on August 28, 2017, Jonathan Leff, a partner of Deerfield Management Company, L.P. and a former
director of the Issuer, exercised in full options to purchase an aggregate of 15,931 shares of Common Stock, on a cashless basis,
for 12,646 shares of Common Stock (based on a $20 per share exercise price, and a closing price of $96.98 per share on the date
of exercise). As previously disclosed, such options were held for the benefit of Deerfield Management Company, L.P., and such shares
were transferred to Deerfield Management Company on September 8, 2017. Such exercise and transfer are referred to in the Schedule
13D as the “Leff Option Exercise.”|
|·||on September 1, 2017, Deerfield International transferred an aggregate of 40,714 shares of Common
Stock to Deerfield Partner at a price of $93.35 per share in a private transaction in connection with fund rebalancing (the “Rebalancing