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Cyclerion investor reports 19.99% stake, board rights

Cyclerion Therapeutics, Inc. (now named Korsana Biosciences, Inc.) received a Schedule 13D from Fairmount Funds Management LLC and affiliates reporting significant ownership and governance rights.

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Form Type
SCHEDULE 13D

Rhea-AI Filing Summary

Cyclerion Therapeutics, Inc. (now named Korsana Biosciences, Inc.) received a Schedule 13D from Fairmount Funds Management LLC and affiliates reporting significant ownership and governance rights. Fairmount, Fairmount Healthcare Fund II L.P., Fairmount Healthcare Co-Invest VI L.P., Peter Harwin and Tomas Kiselak together have voting and dispositive power over 9,103,729 shares of common stock, representing 19.99% of the outstanding common stock as of September 8, 2026. These shares are primarily held through Fund II (6,911,174 shares) and Co-Invest (2,192,555 shares), plus options held by Mr. Kiselak that are exercisable within 60 days.

The group also holds additional upside through Series B Non-Voting Convertible Preferred Stock convertible into 2,074,000 common shares and Pre-Funded Warrants for 66,436 shares, but these are subject to a beneficial ownership limitation of 19.99%, with a potential automatic reduction to 9.99% once Fairmount and its affiliates beneficially own 9.0% or less. The filing details the recently completed reverse-merger with Pre-Merger Korsana, a reverse stock split, and the designation of Series B Preferred Stock, which can elect four “Preferred Directors” with three board votes each and has strong consent rights over major corporate actions.

Fairmount-led funds invested heavily in prior Korsana financings and a $380.0 million pre-closing financing commitment and paid an aggregate $99,999,973 for common stock and pre-funded warrants, plus $12,500,000 for Series B Preferred. The investors are subject to 180-day lock-up agreements after the merger effective time, and the company has agreed under a Registration Rights Agreement to file a resale registration statement within 30 days of the merger closing for the benefit of these investors.

Positive

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Negative

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Filing Explained

The filing reports nominal-price warrants, but their exercise remains capped and raising a ceiling can require 61 days’ notice.

The Schedule 13D reports current beneficial ownership; it does not show the excluded Series B shares or pre-funded warrants already converted into common stock, so this filing discloses no new issuance by itself.

The pre-funded warrants can be exercised at $0.0001 per share, but their applicable ownership ceilings initially range from 4.99% to 14.99%; increasing a ceiling up to 19.99% requires 61 days’ written notice.

Aside from the merger and pre-closing financing, the reporting persons state that they had no common-stock transactions and no present plans for the listed Item 4 actions, while retaining the ability to change their position or seek influence.

The specified developments to monitor are a notice changing a warrant ceiling or an exercise or conversion notice, because either would clarify whether currently excluded securities become common shares.

Beneficial ownership stake 19.99% of common stock Reporting persons’ aggregate ownership based on 45,541,425 shares outstanding as of September 8, 2026
Shares with voting/dispositive power 9,103,729 shares Common shares over which the reporting persons share voting and dispositive power
Fund II common shares 6,911,174 shares Common stock directly held by Fairmount Healthcare Fund II L.P.
Co-Invest common shares 2,192,555 shares Common stock directly held by Fairmount Healthcare Co-Invest VI L.P.
Purchase price – common and warrants $99,999,973 Aggregate purchase price of common stock and Pre-Funded Warrants owned by the reporting persons
Purchase price – Series B Preferred $12,500,000 Aggregate purchase price of Series B Preferred Stock owned by the reporting persons
Korsana Pre-Closing Financing commitment $380.0 million Aggregate commitment under the Subscription Agreement immediately prior to the First Effective Time
Series B conversion ratio 1,000 common shares per preferred share Each Series B Preferred share convertible into 1,000 common shares, subject to limits and adjustments
beneficial ownership limitation regulatory
"The exercise of the Pre-Funded Warrants is subject to a beneficial ownership limitation of 19.99%"
A beneficial ownership limitation is a rule that caps the percentage of a company’s shares an investor can be treated as owning or controlling for voting, regulatory or tax purposes. It matters to investors because it can restrict how many shares a person or group can buy or vote, affect takeover chances, and influence share liquidity and value — like a speed limit that prevents any single driver from taking over the whole road.
Pre-Funded Warrants financial
"66,436 shares of Common Stock issuable upon exercise of Pre-Funded Warrants directly held by Fund II"
Pre-funded warrants are financial instruments that give investors the right to purchase a company's stock at a set price, but with most or all of the purchase price paid upfront. They function like a coupon or gift card for stock, allowing investors to buy shares later at a fixed price, which can be beneficial if they want to avoid future price increases. This makes them important for investors seeking flexibility and certainty in their investment plans.
Series B Non-Voting Convertible Preferred Stock financial
"2,074 shares of Series B Non-Voting Convertible Preferred Stock, no par value per share"
A Series B non-voting convertible preferred stock is a class of company shares that gives holders financial priority—such as fixed dividends and first claim on assets if the company is sold—while not granting voting rights. It can be converted into regular common shares under set conditions, which matters to investors because conversion can increase upside participation but also dilute existing owners; the preference reduces downside risk like a safety buffer.
Lock-up Agreements financial
"entered into lock-up agreements with the Company (the "Lock-up Agreements")"
A lock-up agreement is a contract that prevents company insiders—founders, employees, and early investors—from selling their shares for a set period after a public stock offering. It matters to investors because it keeps a large block of shares off the market temporarily; when the lock-up ends, those holders can sell and this increased supply can cause the stock price to fall, similar to a timed release that suddenly opens a valve.
Registration Rights Agreement regulatory
"entered into a registration rights agreement (the "Registration Rights Agreement")"
A registration rights agreement is a contract that gives investors the option to have their ownership stakes officially registered with the government, making it easier to sell their shares later. This agreement matters because it provides investors with a clearer path to cash out their investments if they choose, offering more liquidity and confidence in their ability to sell their holdings when desired.
Fundamental Transaction financial
"any Fundamental Transaction (as defined in the Articles of Amendment)"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How much of CYCN (Korsana Biosciences, Inc.) do the Fairmount reporting persons own?

The reporting persons collectively have voting and dispositive power over 9,103,729 shares of common stock, representing 19.99% of Cyclerion/Korsana’s outstanding common stock based on 45,541,425 shares outstanding as of September 8, 2026.

How are the CYCN shares held among Fairmount Healthcare Fund II and Co-Invest VI?

Fairmount Healthcare Fund II L.P. directly holds 6,911,174 CYCN common shares, or 15.17% of the class. Fairmount Healthcare Co-Invest VI L.P. directly holds 2,192,555 CYCN common shares, or 4.81% of the class.

What additional CYCN securities could the Fairmount group acquire through convertibles and warrants?

They hold Series B Preferred convertible into 2,074,000 common shares and Pre-Funded Warrants for 66,436 shares. Conversion and exercise are limited by a 19.99% beneficial ownership cap, with potential reduction to 9.99% for the Series B once ownership falls to 9.0% or less.

What did the Fairmount group pay for its CYCN equity and preferred holdings?

The aggregate purchase price for CYCN common stock and Pre-Funded Warrants currently owned is $99,999,973. The aggregate purchase price for the Series B Preferred Stock currently owned is $12,500,000, funded from the reporting persons’ general working capital.

What rights do Series B Preferred holders have at CYCN/Korsana?

While at least 30% of the originally issued Series B Preferred remain outstanding, holders exclusively elect four Preferred Directors, each with three board votes, and must approve specified actions such as certain mergers, charter changes, and additional Series B issuances.

What is the lock-up period affecting the Fairmount holders in CYCN?

Under Lock-up Agreements, certain pre-merger Korsana officers, directors and shareholders, including the reporting persons, agreed not to transfer most CYCN securities for 180 days after the First Effective Time of the merger, subject to limited exceptions.

What registration rights did CYCN grant to the Fairmount investors?

Under a Registration Rights Agreement, CYCN agreed to prepare and file a resale registration statement with the SEC within 30 days after the merger closing and to pay related expenses and provide indemnification to participating securityholders.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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23255M303

(CUSIP Number)
Ms. Erin O'Connor
Fairmount Funds Management LLC, 200 Barr Harbor Drive, Suite 400
West Conshohocken, PA, 19428
(267) 262-5300


Ryan A. Murr, Esq.
Gibson, Dunn & Crutcher LLP, One Embarcadero Center, Suite 2600
San Francisco, CA, 94111
(415) 393-8373

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)
09/08/2026

(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 §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

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).




schemaVersion:


SCHEDULE 13D




Comment for Type of Reporting Person:
The securities include (a) 6,911,174 shares of common stock, no par value per share (the "Common Stock"), directly held by Fairmount Healthcare Fund II L.P. ("Fund II") and 2,192,555 shares of Common Stock directly held by Fairmount Healthcare Co-Invest VI L.P. ("Co-Invest"), and exclude (b) 2,074,000 shares of Common Stock issuable upon conversion of 2,074 shares of Series B Non-Voting Convertible Preferred Stock, no par value per share (the "Series B Preferred Stock"), directly held by Fund II and 66,436 shares of Common Stock issuable upon exercise of Pre-Funded Warrants (as defined in Item 6 and subject to the limitations as described therein) directly held by Fund II. The exercise of the Pre-Funded Warrants is subject to a beneficial ownership limitation of 19.99% of the outstanding shares of Common Stock and the conversion of the Series B Preferred Stock is subject to a beneficial ownership limitation of 19.99% of the outstanding shares of Common Stock. The securities exclude shares of Common Stock issuable upon exercise of Pre-Funded Warrants and conversion of Series B Preferred Stock in excess of such beneficial ownership limitations. At such time as Fairmount Funds Management LLC, a Delaware limited liability company and Securities and Exchange Commission registered investment adviser under the Investment Advisers Act of 1940 ("Fairmount"), and its affiliates beneficially own 9.0% or less of the outstanding shares of Common Stock, the beneficial ownership limitation with respect to the Series B Preferred Stock will automatically reduce to 9.99%. Row 13 is based on 45,544,116 shares of Common Stock outstanding as of September 9, 2026, consisting of (i) 45,541,425 shares of Common Stock outstanding as of September 8, 2026 and (ii) 2,691 shares of Common Stock underlying options that are currently exercisable or will be exercisable within 60 days of the date of this filing by the Reporting Persons.


SCHEDULE 13D




Comment for Type of Reporting Person:
The securities include (a) 6,911,174 shares of Common Stock directly held by Fund II, and exclude (b) 2,074,000 shares of Common Stock issuable upon conversion of 2,074 shares of Series B Preferred Stock directly held by Fund II and 66,436 shares of Common Stock issuable upon exercise of Pre-Funded Warrants directly held by Fund II. The exercise of the Pre-Funded Warrants is subject to a beneficial ownership limitation of 19.99% of the outstanding shares of Common Stock and the conversion of the Series B Preferred Stock is subject to a beneficial ownership limitation of 19.99% of the outstanding shares of Common Stock. The securities exclude shares of Common Stock issuable upon exercise of Pre-Funded Warrants and conversion of Series B Preferred Stock in excess of such beneficial ownership limitations. At such time as Fairmount and its affiliates beneficially own 9.0% or less of the outstanding shares of Common Stock, the beneficial ownership limitation with respect to the Series B Preferred Stock will automatically reduce to 9.99%. Row 13 is based on 45,544,116 shares of Common Stock outstanding as of September 9, 2026, consisting of (i) 45,541,425 shares of Common Stock outstanding as of September 8, 2026 and (ii) 2,691 shares of Common Stock underlying options that are currently exercisable or will be exercisable within 60 days of the date of this filing by the Reporting Persons.


SCHEDULE 13D




Comment for Type of Reporting Person:
The securities include 2,192,555 shares of Common Stock directly held by Co-Invest. Row 13 is based on 45,541,425 shares of Common Stock outstanding as of September 8, 2026.


SCHEDULE 13D




Comment for Type of Reporting Person:
The securities include (a) 6,911,174 shares of Common Stock directly held by Fund II and 2,192,555 shares of Common Stock directly held by Co-Invest, and exclude (b) 2,074,000 shares of Common Stock issuable upon conversion of 2,074 shares of Series B Preferred Stock directly held by Fund II and 66,436 shares of Common Stock issuable upon exercise of Pre-Funded Warrants directly held by Fund II. The exercise of the Pre-Funded Warrants is subject to a beneficial ownership limitation of 19.99% of the outstanding shares of Common Stock and the conversion of the Series B Preferred Stock is subject to a beneficial ownership limitation of 19.99% of the outstanding shares of Common Stock. The securities exclude shares of Common Stock issuable upon exercise of Pre-Funded Warrants and conversion of Series B Preferred Stock in excess of such beneficial ownership limitations. At such time as Fairmount and its affiliates beneficially own 9.0% or less of the outstanding shares of Common Stock, the beneficial ownership limitation with respect to the Series B Preferred Stock will automatically reduce to 9.99%. Row 13 is based on 45,544,116 shares of Common Stock outstanding as of September 9, 2026, consisting of (i) 45,541,425 shares of Common Stock outstanding as of September 8, 2026 and (ii) 2,691 shares of Common Stock underlying options that are currently exercisable or will be exercisable within 60 days of the date of this filing by the Reporting Persons.


SCHEDULE 13D




Comment for Type of Reporting Person:
The securities include (a) 2,691 shares of Common Stock issuable upon the exercise of options that are currently exercisable or will be exercisable within 60 days of the date of this filing held directly by Mr. Kiselak*, (b) 6,911,174 shares of Common Stock directly held by Fund II and (c) 2,192,555 shares of Common Stock directly held by Co-Invest, and exclude (i) 2,074,000 shares of Common Stock issuable upon conversion of 2,074 shares of Series B Preferred Stock directly held by Fund II and (ii) 66,436 shares of Common Stock issuable upon exercise of Pre-Funded Warrants directly held by Fund II. The exercise of the Pre-Funded Warrants is subject to a beneficial ownership limitation of 19.99% of the outstanding shares of Common Stock and the conversion of the Series B Preferred Stock is subject to a beneficial ownership limitation of 19.99% of the outstanding shares of Common Stock. The securities exclude shares of Common Stock issuable upon exercise of Pre-Funded Warrants and conversion of Series B Preferred Stock in excess of such beneficial ownership limitations. At such time as Fairmount and its affiliates beneficially own 9.0% or less of the outstanding shares of Common Stock, the beneficial ownership limitation with respect to the Series B Preferred Stock will automatically reduce to 9.99%. Row 13 is based on 45,544,116 shares of Common Stock outstanding as of September 9, 2026, consisting of (i) 45,541,425 shares of Common Stock outstanding as of September 8, 2026 and (ii) 2,691 shares of Common Stock underlying options that are currently exercisable or will be exercisable within 60 days of the date of this filing by the Reporting Persons. * Under Mr. Kiselak's arrangement with Fairmount, Mr. Kiselak holds the options for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). Mr. Kiselak is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. Mr. Kiselak therefore disclaims beneficial ownership of the option and underlying common stock.


SCHEDULE 13D


Fairmount Funds Management LLC
Signature:/s/ Peter Harwin
Name/Title:Peter Harwin, Managing Member
Date:09/11/2026
Signature:/s/ Tomas Kiselak
Name/Title:Tomas Kiselak, Managing Member
Date:09/11/2026
Fairmount Healthcare Fund II L.P.
Signature:/s/ Peter Harwin
Name/Title:Peter Harwin, Managing Member
Date:09/11/2026
Signature:/s/ Tomas Kiselak
Name/Title:Tomas Kiselak, Managing Member
Date:09/11/2026
Fairmount Healthcare Co-Invest VI L.P.
Signature:/s/ Peter Harwin
Name/Title:Peter Harwin, Managing Member
Date:09/11/2026
Signature:/s/ Tomas Kiselak
Name/Title:Tomas Kiselak, Managing Member
Date:09/11/2026
Peter Evan Harwin
Signature:/s/ Peter Harwin
Name/Title:Peter Harwin
Date:09/11/2026
Tomas Kiselak
Signature:/s/ Tomas Kiselak
Name/Title:Tomas Kiselak
Date:09/11/2026

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