13D Filing: Caxton Corp and Strongbridge Biopharma PLC (SBBP)

 

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of
1934

(Amendment No. 1)

Strongbridge Biopharma plc

(Name of Issuer)

Ordinary Shares, $0.01 par value

(Title of Class of Securities)

G85347105

(CUSIP Number)

Mr. Heath N. Weisberg

Caxton Corporation

731 Alexander Road, Bldg. 2, Suite 500

Princeton, New Jersey 08540

(212) 205-6805

(Name, Address and Telephone Number of
Person Authorized to

Receive Notices and Communications)

April 29, 2017

(Date of Event which Requires Filing
of this Statement)

If the filing person has previously filed a statement on
Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Section
240.13d-1(e), 240.13d-1(f) or

240.13d-1(g), check the following box. | |

Note: Schedules filed in paper format shall include a signed
original and five copies of the schedule, including all exhibits. See Section

240.13d-7 for other parties to whom copies are to be sent.

*The remainder of this cover page shall be filled out for
a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment
containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page
shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”)
or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however,
see the Notes).