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SCHEDULE 13D/A 0001352546 XXXXXXXX LIVE 11 Common Stock, par value $0.01 per share 02/27/2026 false 0001374690 517125100 Larimar Therapeutics, Inc. THREE BALA PLAZA EAST SUITE 506 BALA CYNWYD PA 19004 Deerfield Management Company 212-551-1600 345 Park Avenue, 12th Floor New York NY 10010 Jonathan D. Weiner, Esq. 212-940-8800 Katten Muchin Rosenman LLP 50 Rockefeller Plaza New York NY 10020 Mark D. Wood, Esq. 212-940-8800 Katten Muchin Rosenman LLP 50 Rockefeller Plaza New York NY 10020 0001603333 N Deerfield Private Design Fund III, L.P. b WC N DE 0.00 10622928.00 0.00 10622928.00 10622928.00 N 10.25 PN 0001646981 N Deerfield Healthcare Innovations Fund, L.P. b WC N DE 0.00 8153107.00 0.00 8153107.00 8153107.00 N 7.87 PN 0001680307 N Deerfield Private Design Fund IV, L.P. b WC N DE 0.00 10622957.00 0.00 10622957.00 10622957.00 N 10.25 PN 0001301041 N Deerfield Partners, L.P. b WC N DE 0.00 6207982.00 0.00 6207982.00 6207982.00 N 5.99 PN 0001610540 N Deerfield Mgmt III, L.P. b AF N DE 0.00 10622928.00 0.00 10622928.00 10622928.00 N 10.25 PN Comprised of shares of common stock held by Deerfield Private Design Fund III, L.P., of which Deerfield Mgmt III, L.P. is the general partner. 0001665736 N Deerfield Mgmt HIF, L.P. b AF N DE 0.00 8153107.00 0.00 8153107.00 8153107.00 N 7.87 PN Comprised of shares of common stock held by Deerfield Healthcare Innovations Fund, L.P., of which Deerfield Mgmt HIF, L.P. is the general partner. 0001713467 N Deerfield Mgmt IV, L.P. b AF N DE 0.00 10622957.00 0.00 10622957.00 10622957.00 N 10.25 PN Comprised of shares of common stock held by Deerfield Private Design Fund IV, L.P., of which Deerfield Mgmt IV, L.P. is the general partner. 0001010823 N Deerfield Mgmt, L.P. b WC N DE 0.00 6207982.00 0.00 6207982.00 6207982.00 N 5.99 PN Comprised of shares of common stock held by Deerfield Partners, L.P., of which Deerfield Mgmt, L.P. is the general partner. 0001009258 N Deerfield Management Company, L.P. b AF Y DE 0.00 35667474.00 0.00 35667474.00 35667474.00 N 34.41 PN Comprised of (i) an aggregate of 35,606,974 shares of common stock held by Deerfield Private Design Fund III, L.P., Deerfield Private Design Fund IV, L.P., Deerfield Healthcare Innovations Fund, L.P. and Deerfield Partners, L.P., of which Deerfield Management Company, L.P. is the investment manager and (ii) an aggregate of 60,500 shares of common stock issuable upon exercise of options (the "Leff Options") held by Jonathan Leff, an employee of Deerfield Management Company, L.P., for the benefit, and subject to the direction, of Deerfield Management Company, L.P. The Leff Options consist options that were granted to Mr. Leff on July 16, 2020, May 12, 2021, May 10, 2022, May 9, 2023 and May 29, 2024, each of which is fully vested. 0001352546 N James E. Flynn b AF N X1 0.00 35667474.00 0.00 35667474.00 35667474.00 N 34.41 IN Comprised of (i) an aggregate of 35,606,974 shares of common stock held by Deerfield Private Design Fund III, L.P., Deerfield Private Design Fund IV, L.P., Deerfield Healthcare Innovations Fund, L.P. and Deerfield Partners, L.P., of which Deerfield Management Company, L.P. is the investment manager and (ii) an aggregate of 60,500 shares of common stock issuable upon exercise of options (the "Leff Options") held by Jonathan Leff, an employee of Deerfield Management Company, L.P., for the benefit, and subject to the direction, of Deerfield Management Company, L.P. The Leff Options consist options that were granted to Mr. Leff on July 16, 2020, May 12, 2021, May 10, 2022, May 9, 2023 and May 29, 2024, each of which is fully vested. Mr. Flynn is the sole manager of the general partner of each of Deerfield Mgmt III, L.P., Deerfield Mgmt IV, L.P., Deerfield Mgmt HIF, L.P., Deerfield Mgmt, L.P. and Deerfield Management Company, L.P. Common Stock, par value $0.01 per share Larimar Therapeutics, Inc. THREE BALA PLAZA EAST SUITE 506 BALA CYNWYD PA 19004 This Amendment No. 11 (this "Amendment") to Schedule 13D is filed by (i) Deerfield Private Design Fund III, L.P. ("Deerfield Private Design Fund III"), (ii) Deerfield Healthcare Innovations Fund, L.P. ("Deerfield Healthcare Innovations Fund"), (iii) Deerfield Private Design Fund IV, L.P. ("Deerfield Private Design Fund IV"), (iv) Deerfield Partners, L.P. ("Deerfield Partners"), (v) Deerfield Mgmt III, L.P. ("Deerfield Mgmt III"), (vi) Deerfield Mgmt HIF, L.P. ("Deerfield Mgmt HIF"), (vii) Deerfield Mgmt IV, L.P. ("Deerfield Mgmt IV"), (viii) Deerfield Mgmt, L.P. ("Deerfield Mgmt"), (ix) Deerfield Management Company, L.P. ("Deerfield Management") and (x) James E. Flynn ("Flynn" and, together with Deerfield Private Design Fund III, Deerfield Healthcare Innovations Fund, Deerfield Private Design Fund IV, Deerfield Partners, Deerfield Mgmt III, Deerfield Mgmt HIF, Deerfield Mgmt IV, Deerfield Mgmt and Deerfield Management, the "Reporting Persons"), with respect to the securities of Larimar Therapeutics, Inc. (as amended by Amendment No.1, Amendment No. 2, Amendment No. 3, Amendment No. 4, Amendment No. 5, Amendment No. 6, Amendment No. 7, Amendment No. 8, Amendment No. 9, Amendment No. 10 and this Amendment No. 11, the "Schedule 13D"). Deerfield Private Design Fund III, Deerfield Healthcare Innovations Fund, Deerfield Private Design Fund IV and Deerfield Partners are collectively referred to herein as the "Funds". Capitalized terms used herein but not otherwise defined herein shall have the meanings ascribed to them in the Schedule 13D. Item 3 of the Schedule 13D is hereby amended by adding the following: On February 27, 2026, Deerfield Private Design Fund III, Deerfield Private Design Fund IV, Deerfield Healthcare Innovations Fund and Deerfield Partners purchased 1,084,010, 1,084,012, 831,978 and 2,000,000 shares of Common Stock (collectively, the "February 2026 Shares"), respectively, at a price of $5.00 per share, or aggregate purchase prices of $5,420,050, $5,420,060, $4,159,890 and $10,000,000, respectively. Each Fund utilized available cash assets to acquire the February 2026 Shares. Item 4 of the Schedule 13D is hereby amended by adding the following: Each Fund acquired its February 2026 Shares for investment purposes in an underwritten offering conducted by the Company (the "February 2026 Offering") pursuant to the Prospectus Supplement, dated as of February 25, 2026, to the Issuer's Prospectus, dated as of May 24, 2024 (the "February 2026 Offering"). Items 5(a), 5(b) and 5(c) of the Schedule 13D are hereby amended and restated in their entirety to read as follows: (1) Deerfield Private Design Fund III Number of shares: 10,622,928 Percentage of shares: 10.25%* (2) Deerfield Healthcare Innovations Fund Number of shares: 8,153,107 Percentage of shares: 7.87%* (3) Deerfield Private Design Fund IV Number of shares: 10,622,957 Percentage of shares: 10.25%* (4) Deerfield Partners Number of shares: 6,207,982 Percentage of shares: 5.99%* (5) Deerfield Mgmt III Number of shares: 10,622,928 (comprised of shares held by Deerfield Private Design Fund III) Percentage of shares: 10.25%* (6) Deerfield Mgmt HIF Number of shares: 8,153,107 (comprised of shares held by Deerfield Healthcare Innovations Fund) Percentage of shares: 7.87%* (7) Deerfield Mgmt IV Number of shares: 10,622,957 (comprised of shares held by Deerfield Private Design Fund) Percentage of shares: 10.25%* (8) Deerfield Mgmt Number of shares: 6,207,982 (comprised of shares held by Deerfield Partners) Percentage of shares: 5.99%* (9) Deerfield Management Number of shares: 35,667,474 (comprised of shares held by Deerfield Private Design Fund III, Deerfield Private Design Fund IV, Deerfield Healthcare Innovations Fund, Deerfield Partners and shares underlying options held by Jonathan Leff at the direction and for the benefit of Deerfield Management) Percentage of shares: 34.41%* (10) James E. Flynn Number of shares: 35,667,474 (comprised of shares held by Deerfield Private Design Fund III, Deerfield Private Design Fund IV, Deerfield Healthcare Innovations Fund, Deerfield Partners and shares underlying options held by Jonathan Leff at the direction and for the benefit of Deerfield Management) Percentage of shares: 34.41%* * Throughout this report, the percentage of outstanding Common Stock beneficially owned by the Reporting Persons reflects 103,590,392 shares of Common Stock outstanding, including shares issued in the February 2026 Offering, based on information set forth in the Prospectus Supplement, dated as of February 25, 2026, filed by the Company with the Securities and Exchange Commission on February 26, 2026. Items 5(a), 5(b) and 5(c) of the Schedule 13D are hereby amended and restated in their entirety to read as follows: (1) Deerfield Private Design Fund III Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 10,622,928 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 10,622,928 (2) Deerfield Healthcare Innovations Fund Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 8,153,107 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 8,153,107 (3) Deerfield Private Design Fund IV Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 10,622,957 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 10,622,957 (4) Deerfield Partners Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 6,207,982 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 6,207,982 (5) Deerfield Mgmt III Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 10,622,928 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 10,622,928 (6) Deerfield Mgmt HIF Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 8,153,107 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 8,153,107 (7) Deerfield Mgmt IV Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 10,622,957 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 10,622,957 (8) Deerfield Mgmt Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 6,207,982 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 6,207,982 (9) Deerfield Management Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 35,667,474 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 35,667,474 (10) James E. Flynn Sole power to vote or direct the vote: 0 Shared power to vote or direct the vote: 35,667,474 Sole power to dispose or to direct the disposition: 0 Shared power to dispose or direct the disposition: 35,667,474 James E. Flynn is the sole manager of the general partner of each of Deerfield Mgmt III, Deerfield Mgmt IV, Deerfield Mgmt HIF, Deerfield Mgmt, and Deerfield Management. Deerfield Mgmt III is the general partner of Deerfield Private Design Fund III. Deerfield Mgmt HIF is the general partner of Deerfield Healthcare Innovations Fund. Deerfield Mgmt IV is the general partner of Deerfield Private Design Fund IV. Deerfield Mgmt is the general partner of Deerfield Partners. Deerfield Management is the investment manager of each of Deerfield Private Design Fund III, Deerfield Healthcare Innovations Fund, Deerfield Private Design Fund IV and Deerfield Partners. Items 5(a), 5(b) and 5(c) of the Schedule 13D are hereby amended and restated in their entirety to read as follows: Except as set forth in Item 3 of this Schedule 13D, no Reporting Person has effected any transactions in the Common Stock during the past 60 days. Deerfield Private Design Fund III, L.P. /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026 Deerfield Healthcare Innovations Fund, L.P. /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026 Deerfield Private Design Fund IV, L.P. /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026 Deerfield Partners, L.P. /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026 Deerfield Mgmt III, L.P. /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026 Deerfield Mgmt HIF, L.P. /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026 Deerfield Mgmt IV, L.P. /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026 Deerfield Mgmt, L.P. /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026 Deerfield Management Company, L.P. /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026 James E. Flynn /s/ Jonathan Isler Jonathan Isler, Attorney-in-Fact 03/02/2026