UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): September 21, 2018

RA PHARMACEUTICALS, INC.

(Exact name of Registrant as Specified in Its Charter)

(617) 401-4060

(Registrant’s telephone number, include area code)

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions

o                                    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o                                    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o                                    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o                                    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company  x

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. x

Item 5.02. Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

On September 21, 2018, the Board of Directors (the “Board”) of Ra Pharmaceuticals, Inc. (the “Company”) elected Aoife M. Brennan, M.B., B.Ch. as a Class III director of the Company. Dr. Brennan has been appointed to serve on the Audit Committee of the Board (the “Audit Committee”).

Dr. Brennan will participate in the Company’s standard compensation program for non-employee directors, including an annual retainer of $35,000, an additional annual retainer of $7,500 for Dr. Brennan’s service on the Audit Committee, and an initial award of options to purchase 25,000 shares of the Company’s common stock (the “Initial Award”). The Initial Award has an exercise price equal to $16.36, the fair market value of a share of the Company’s common stock on the date of grant, and will vest and become exercisable in three substantially equal annual installments occurring on each of the first three anniversaries of the grant date, subject to Dr. Brennan’s continued service on the Board through each such vesting date. Dr. Brennan has also entered into the Company’s standard indemnification agreement for directors and officers.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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