13D Filing: RA Capital Management and Biocryst Pharmaceuticals Inc (BCRX)

Item 5.

Interest in Securities of the Issuer.

The aggregate percentage
of Shares reported owned by each Reporting Person is based upon 98,606,110 Shares outstanding, which is the total number of Shares
outstanding as of January 31, 2018, as reported in the Issuer’s Annual Report on Form 10-K/A, filed with the Securities and
Exchange Commission on March 27, 2018.

Item 5(a)-(b) See
Items 7-11 of the cover pages and Item 2 of this Statement.

Item 5(c) of the Statement
is hereby amended and supplemented by adding the following:

(c) The Reporting
Persons have not entered into any transactions in the Shares during the past sixty days.

(d) No person other
than the Reporting Persons is known to have the right to receive, or the power to direct the receipt of dividends from, or proceeds
from the sale of, the Shares.

(e) Not Applicable.

Item 6.

Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

On April 2, 2018,
the Reporting Persons entered into a Joint Filing Agreement in which the Reporting Persons agreed to the joint filing on behalf
of each of them of statements on Schedule 13D with respect to the securities of the Issuer to the extent required by applicable
law. The Joint Filing Agreement is attached hereto as Exhibit 99.2 and is incorporated herein by reference.

Other than as described
herein, there are no contracts, arrangements, understandings or relationships among the Reporting Persons, or between the Reporting
Persons and any other person, with respect to the securities of the Issuer.

Item 7.

Material to be Filed as Exhibits.

99.1

Letter to the Board of Directors, dated April 2, 2018.

99.2

Joint Filing Agreement by and between RA Capital Management, LLC and Peter Kolchinsky, dated April 2, 2018.