UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D. C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. )*

Portola Pharmaceuticals, Inc.

(Name of Issuer)

Common Stock, par value $0.001

(Title of Class of Securities)

737010108

(CUSIP Number of Class of Securities)

Alec N. Litowitz

Magnetar Capital LLC

1603 Orrington Ave.

Evanston, Illinois 60201

(847) 905-4400

(Name, Address and Telephone Number of Person Authorized
to Receive Notices and Communications)

May 5, 2020

(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 Rule 13d-1(e), 13d-1(f) or 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 Rule 240.13d-7(b) 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).

CUSIP No. 737010108

SCHEDULE 13D

Page 2 of 10

1. NAME OF REPORTING PERSON:

Magnetar Financial LLC

2. CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) o

(b) x

3. SEC USE ONLY

4. SOURCE OF FUNDS

5. CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) o

6. CITIZENSHIP OR PLACE OF ORGANIZATION

Delaware

NUMBER OF

7. SOLE VOTING POWER

BENEFICIALLY

OWNED BY

8. SHARED VOTING POWER

4,106,528

EACH REPORTING

PERSON

9. SOLE DISPOSITIVE POWER

WITH

10. SHARED DISPOSITIVE POWER

4,106,528

11. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

4,106,528

12. CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

13. PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

5.23%

14. TYPE OF REPORTING PERSON

IA; OO

CUSIP No. 737010108

SCHEDULE 13D

Page 3 of 10

1. NAME OF REPORTING PERSON:

Magnetar Capital Partners LP

2. CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) o

(b) x

3. SEC USE ONLY

4. SOURCE OF FUNDS

5. CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) o

6. CITIZENSHIP OR PLACE OF ORGANIZATION

Delaware

NUMBER OF

7. SOLE VOTING POWER

BENEFICIALLY

OWNED BY

8. SHARED VOTING POWER

4,106,528

EACH REPORTING

PERSON

9. SOLE DISPOSITIVE POWER

WITH

10. SHARED DISPOSITIVE POWER

4,106,528

11. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

4,106,528

12. CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

13. PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

5.23%

14. TYPE OF REPORTING PERSON

HC; OO

CUSIP No. 737010108

SCHEDULE 13D

Page 4 of 10

1. NAME OF REPORTING PERSON:

Supernova Management LLC

2. CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) o

(b) x

3. SEC USE ONLY

4. SOURCE OF FUNDS

5. CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) o

6. CITIZENSHIP OR PLACE OF ORGANIZATION

Delaware

NUMBER OF

7. SOLE VOTING POWER

BENEFICIALLY

OWNED BY

8. SHARED VOTING POWER

4,106,528

EACH REPORTING

PERSON

9. SOLE DISPOSITIVE POWER

WITH

10. SHARED DISPOSITIVE POWER

4,106,528

11. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

4,106,528

12. CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

13. PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

5.23%

14. TYPE OF REPORTING PERSON

HC; OO

CUSIP No. 737010108

SCHEDULE 13D

Page 5 of 10

1. NAME OF REPORTING PERSON:

Alec N. Litowitz

2. CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) o

(b) x

3. SEC USE ONLY

4. SOURCE OF FUNDS

5. CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) o

6. CITIZENSHIP OR PLACE OF ORGANIZATION

United States of America

NUMBER OF

7. SOLE VOTING POWER

BENEFICIALLY

OWNED BY

8. SHARED VOTING POWER

4,106,528

EACH REPORTING

PERSON

9. SOLE DISPOSITIVE POWER

WITH

10. SHARED DISPOSITIVE POWER

4,106,528

11. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

4,106,528

12. CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

13. PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

5.23%

14. TYPE OF REPORTING PERSON

HC; IN

SCHEDULE 13D

ITEM 1. SECURITY AND ISSUER

This Schedule 13D (this “Statement”) relates to the shares of common stock, par value $0.001 (the “Shares”), of Portola Pharmaceuticals, Inc., a Delaware corporation (the “Company”). The principal executive offices of the Company are located at 270 E. Grand Avenue, South San Francisco, California 94080.

ITEM 2. IDENTITY AND BACKGROUND

(a) The persons filing this Statement are Magnetar Financial LLC, a Delaware limited liability company (“Magnetar Financial”), Magnetar Capital Partners LP, a Delaware0 limited partnership (“Magnetar Capital Partners”), Supernova Management LLC, a Delaware limited liability company (“Supernova Management”), and Alec N. Litowitz (“Mr. Litowitz”) (collectively, the “Reporting Persons”).

This Statement relates to Shares held for the accounts of each of (i) Magnetar Capital Master Fund, Ltd, a Cayman Islands exempted company (“Magnetar Capital Master Fund”), (ii) Magnetar PRA Master Fund Ltd, a Cayman Islands exempted company (“PRA Master Fund”), (iii) Magnetar Constellation Fund II-PRA LP, a Delaware limited partnership (“Constellation Fund”), and (iv) Magnetar Systematic Multi-Strategy Master Fund Ltd, a Cayman Islands exempted company, (“Systematic Master Fund”), collectively (the “Funds”).

Magnetar Financial is a Securities and Exchange Commission (“SEC”) registered investment adviser under Section 203 of the Investment Advisers Act of 1940, as amended, and manager of investment funds and managed accounts. Magnetar Financial serves as investment adviser to each of the Funds. In such capacity, Magnetar Financial exercises voting and investment power over the Shares held for the accounts of each of the Funds. Magnetar Capital Partners serves as the sole member and parent holding company of Magnetar Financial. Supernova Management is the general partner of Magnetar Capital Partners. The manager of Supernova Management is Mr. Litowitz.

(b) The business address of each of the Reporting Persons is 1603 Orrington Avenue, 13th Floor, Evanston, Illinois 60201.

(c) Each of the Funds is a private investment fund; Magnetar Financial is a privately-held SEC registered investment adviser and manager of investment funds and managed accounts; Magnetar Capital Partners is a privately-held limited partnership and serves as the sole member and parent holding company of Magnetar Financial; Supernova Management is a privately-held limited liability company and is the general partner of Magnetar Capital Partners; and Mr. Litowitz is a citizen of the United States of America, manager of Supernova Management and Chief Executive Officer of Magnetar Financial.

(d) None of the Reporting Persons has, during the last five years, been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e) None of the Reporting Persons has, during the last five years, been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction as a result of which such Reporting Person was or is subject to a judgment, decree or final order enjoining future violations

of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f) Magnetar Financial is a Delaware limited liability company. Magnetar Capital Partners is a Delaware limited partnership. Supernova Management is a Delaware limited liability company. Mr. Litowitz is a citizen of the United States of America.

ITEM 3. SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION

The aggregate amount of funds used by the Reporting Persons in purchasing the 4,108,242 Shares reported herein on behalf of the Funds have come directly from the assets of the Funds, which may at any given time, have included margin loans made by brokerage firms in the ordinary course of business. The aggregate amount of funds used by the Reporting Persons in purchasing the Shares on behalf of the Funds was $73,192,514 (excluding commissions and other execution-related costs).

ITEM 4. PURPOSE OF TRANSACTION

The Reporting Persons acquired the 4,106,528 Shares reported herein on behalf of the Funds after the public announcement of the Merger Agreement (as defined below) for purposes of receiving the merger consideration described below upon consummation of the Merger (as described below).

The Reporting Persons acquired the 1,714 Shares reported herein on behalf of Systematic Master Fund to cover a pre-existing short position in a strategy unrelated to the passive risk arbitrage strategy.

Each of the Reporting Persons reserves the right to acquire additional securities of the Company in the open market, in privately negotiated transactions, or otherwise, to dispose of all or a portion of the Shares and/or other securities reported in this Statement, or to change their intention with respect to any or all of the matters referred to in this Item 4.

Other than as described above in this Item 4, the Reporting Persons do not have any plans or proposals that relate to, or would result in, any actions or events specified in clauses (a) through (j) of Item 4 to Schedule 13D.

ITEM 5. INTEREST IN SECURITIES OF THE ISSUER

The Company reported in their Schedule 14A filed on April 20, 2020 that 78,484,617 Shares were issued and outstanding as of April 17, 2020.

(a) As of May 6, 2020, each of the Reporting Persons may have been deemed to have beneficial ownership of 4,106,528 Shares, which consisted of (i) 89,082 Shares held for the benefit of Magnetar Capital Master Fund, (ii) 1,964,720 Shares held for the benefit of PRA Master Fund, (iii) 1,936,582 Shares held for the benefit of Constellation Fund; and (iv) 116,144 Shares held for the benefit of Systematic Master Fund, and all such Shares represented beneficial ownership of approximately 5.23% of the Shares.

(b) As of May 6, 2020, each of the Reporting Persons may have been deemed to share the power to vote and direct the disposition of 4,106,528 Shares, which consisted of (i) 89,082 Shares held for the benefit of Magnetar Capital Master Fund, (ii) 1,964,720 Shares held for the benefit of PRA Master Fund, (iii) 1,936,582 Shares held for the benefit of Constellation Fund; and (iv) 116,144 Shares held for the benefit of Systematic Master Fund, and all such Shares represented beneficial ownership of approximately 5.23% of the Shares.

(c) Except as set forth on Schedule A attached hereto and Item 6, the Funds had no transactions in the Shares during the 60 days preceding the date of filing of this Statement. All of the transactions set forth on Schedule A attached hereto were effected in the ordinary course of business of Magnetar Financial for the accounts of each of the Funds. The transactions in the Shares set forth on Schedule A were effected in open market transactions on NASDAQ and various other trading markets.

As disclosed by the Company in the 8-K filed with the SEC on May 5, 2020:

On My 5, 2020, Alexion Pharmaceuticals, Inc. and Portola Pharmaceuticals, Inc. announced that they have entered into a definitive merger agreement for Alexion to acquire Portola, a commercial-stage biopharmaceutical company focused on life-threatening blood-related disorders. Under the terms of the merger agreement, a subsidiary of Alexion will commence a tender offer to acquire all of the outstanding shares of Portola’s common stock at a price of $18 per share in cash. The tender offer is subject to customary conditions, including the tender of a majority of the outstanding shares of Portola common stock, the expiration or termination of the waiting period under the Hart-Scott Rodino Antitrust Improvements Act of 1976 and receipt of certain other regulatory approvals. Following successful completion of the tender offer, Alexion will acquire all remaining shares not tendered in the offer at the same price of $18 per share through a merger. The transaction is expected to close in the third quarter of 2020.

(d) No other person is known by the Reporting Persons to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, any Shares that are beneficially owned by the Reporting Persons.

ITEM 6. CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT TO THE SECURITIES OF THE ISSUER

Pursuant to Rule 13d-1(k)(1) promulgated under the Securities Exchange Act of 1934, as amended, the Reporting Persons have entered into an agreement with respect to the joint filing of this Statement, and any amendment or amendments hereto.

Certain clients of Magnetar Financial have entered into total return swap agreements giving them economic exposure to the Company.

The 964 Shares were sold short on behalf of Systematic Master Fund in a strategy unrelated to the passive risk arbitrage strategy and they were obtained from prime brokers pursuant to customary securities lending agreements.

Magnetar Asset Management LLC (“Magnetar Asset Management”) is a SEC registered investment adviser and an affiliate of Magnetar Financial. Magnetar Capital Partners serves as the sole member and parent holding company of Magnetar Asset Management. Certain clients of Magnetar Asset Management have entered into total return swap agreements giving them economic exposure to the Company.

Except as otherwise described herein, no contracts, arrangements, understandings or similar relationships exist with respect to the securities of the Company among or between the Reporting Persons or any other person or entity.

ITEM 7. MATERIAL TO BE FILED AS EXHIBITS

Exhibit No.	Description

99.1	Joint Filing Agreement, dated as of May 8, 2020 among the Reporting Persons.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: May 8, 2020

MAGNETAR FINANCIAL LLC

By: Magnetar Capital Partners LP, its Sole Member


By:	/s/ Alec N. Litowitz
	Name:	Alec N. Litowitz
	Title:	Manager of Supernova Management LLC, the General Partner of Magnetar Capital Partners LP

MAGNETAR CAPITAL PARTNERS LP


By:	/s/ Alec N. Litowitz
	Name:	Alec N. Litowitz
	Title:	Manager of Supernova Management LLC, the General Partner of Magnetar Capital Partners LP

SUPERNOVA MANAGEMENT LLC


By:	/s/ Alec N. Litowitz
	Name:	Alec N. Litowitz
	Title:	Manager


/s/ Alec N. Litowitz
Alec N. Litowitz

SCHEDULE A

Funds

Date	Number of Shares Bought	Price Per Share($) (1)(2)
5/4/2020	1,576	7.41476(3)
5/5/2020	4,064,668	17.80766 (4)
5/6/2020	41,998	17.80617 (5)

(1)Excludes commissions and other execution-related costs.

(2) Upon request by the staff of the Securities and Exchange Commission, full information regarding the number of shares bought or sold (as the case may be) at each separate price will be provided.

(3) Reflects a weighted average purchase price of $7.41476 per share, at prices ranging from $7.260 to $7.750 per share.

(4) Reflects a weighted average purchase price of $ 17.80766 per share, at prices ranging from $17.710 to $17.910 per share.

(5) Reflects a weighted average purchase price of $ 17.80617 per share, at prices ranging from $17.790 to $17.820 per share.

Systematic Master Fund

Date

Number of Shares Sold

Price Per Share($) (1)(2)

04/02/2020

(820)

7.01053(3)

04/03/2020

(144)

6.74667(4)

(1)Excludes commissions and other execution-related costs.

(2) Upon request by the staff of the Securities and Exchange Commission, full information regarding the number of shares bought or sold (as the case may be) at each separate price will be provided.

(3) Reflects a weighted average purchase price of $7.01053 per share, at prices ranging from $6.820 to $7.220 per share.

(4) Reflects a weighted average purchase price of $6.74667 per share, at prices ranging from $6.440 to $7.040 per share.

EXHIBIT INDEX

Exhibit No.		Description


99.1		Joint Filing Agreement, dated as of May 8, 2020, among the Reporting Persons.