Material Agreement, Financial Obligation, Private Placement (Form 8-K)

Item 1.01 Entry into a Material Agreement.

Indenture and Notes

On June 10, 2026 (the "Closing Date"), Syndax Pharmaceuticals, Inc. (the "Company") issued $250.0 million aggregate principal amount of 2.25% Convertible Senior Notes due 2031 (the "Notes") in a private placement (the "Private Placement") pursuant to the previously announced privately negotiated subscription agreements. The Notes were issued pursuant to an indenture, dated as of the Closing Date (the "Indenture"), between the Company and U.S. Bank Trust Company, National Association, as trustee.

The terms of the Notes and Indenture are described in Item 1.01 on Form 8-K filed by the Company on June 4, 2026, which information is incorporated herein by reference.

Copies of the Indenture and the form of the Notes are attached as Exhibit 4.1 and 4.2, respectively, to this Current Report on Form 8-K and are incorporated herein by reference (and the foregoing description is qualified in its entirety by reference to such documents).

Proceeds

The Company's net proceeds from the Private Placement were approximately $243.0 million, after deducting the placement agent's fees and Private Placement expenses payable by the Company. The Company expects to use the net proceeds from the Private Placement for general corporate purposes, including working capital, research and development expenditures, commercialization activity expenditures and business development expenditures.

Item 2.03 Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant.

The information set forth under Item 1.01 of this Current Report on Form 8-K is incorporated herein by reference.

Item 3.02 Unregistered Sale of Equity Securities.

The information set forth under Item 1.01 of this Current Report on Form 8-K is incorporated herein by reference.

The Company offered and sold the Notes to certain investors in reliance on the exemption from registration provided by Section 4(a)(2) of the Securities Act of 1933, as amended (the "Securities Act"). The Company relied on this exemption from registration based in part on representations made by each investor in the subscription agreements, dated June 3, 2026, between the Company and each investor identified therein.

The Notes and the shares of Common Stock issuable upon conversion of the Notes, if any, have not been registered under the Securities Act and may not be offered or sold in the United States absent registration or an applicable exemption from registration requirements.

To the extent that any shares of Common Stock are issued upon conversion of the Notes, they will be issued in transactions anticipated to be exempt from registration under the Securities Act by virtue of Section 3(a)(9) thereof as involving an exchange by the Company exclusively with its noteholders because no commission or other remuneration is expected to be paid in connection with conversion of the Notes and any resulting issuance of shares of Common Stock. Initially, a maximum of 13,631,400 shares of Common Stock may be issued upon conversion of the Notes based on the initial maximum conversion rate of 54.5256 shares of Common Stock per $1,000 principal amount of Notes, which is subject to customary anti-dilution adjustment provisions.