What do the RSU-related footnotes in Moleculin Biotech (MBRX) CFO’s Form 4 explain?

The footnotes explain RSUs convert into common stock one-for-one and detail prior RSU grants. They note grants of 434 RSUs on June 20, 2022 and 693 RSUs on June 22, 2023, vesting in four equal annual installments starting one year after each grant date.

How are Moleculin Biotech (MBRX) Series E warrants related to the CFO’s reported holdings?

The filing states the CFO’s holdings include 100,003 shares underlying Series E warrants. These warrants give the right to purchase additional Moleculin Biotech common shares, contributing to the total 147,718 derivative securities reported as held following the June 2026 transactions.

Moleculin CFO exercises RSUs, withholds shares for tax

Moleculin Biotech, Inc. Chief Financial Officer Jonathan P. Foster reported routine equity compensation activity involving restricted stock units and related tax withholding.

Filing Impact

(Neutral)

Filing Sentiment

(Neutral)How Sentiment works

Sentiment and the balance of points

Rhea-AI Sentiment reads the wording of the document, how positive or negative its language is on a 1 to 5 scale. The balance of points shown with the takes weighs what the document actually discloses, so the two can disagree, for example when a trial that missed its main goal is described in upbeat language.

How Sentiment works How the balance works

Form Type

Rhea-AI Filing Summary

Moleculin Biotech, Inc. Chief Financial Officer Jonathan P. Foster reported routine equity compensation activity involving restricted stock units and related tax withholding. On June 20 and June 22, 2026, restricted stock units converted into a total of 283 shares of common stock at a conversion price of $0.00 per share.

To cover tax obligations on these vestings, 72 shares of common stock were disposed of at prices of $2.88 and $3.12 per share through tax-withholding dispositions, not open-market sales. Following these transactions, Foster directly holds 12,340 shares of common stock and 147,718 derivative securities, which include 100,003 shares of common stock underlying Series E warrants.

Insider Trade Summary

283 shares exercised/converted

Exercise 6 txns

Insider Foster Jonathan P.

Role Chief Financial Officer

Type	Security	Shares	Price	Value
Exercise	Restricted Stock Units	174	$0.00	$0.00
Exercise	Common Stock	174	$0.00	$0.00
Exercise Price or Tax Liability	Common Stock	41	$3.12	$127.92
Exercise	Restricted Stock Units	109	$0.00	$0.00
Exercise	Common Stock	109	$0.00	$0.00
Exercise Price or Tax Liability	Common Stock	31	$2.88	$89.28

Holdings After Transaction: Restricted Stock Units — 147,718 contracts (Direct); Common Stock — 12,340 shares (Direct)

Footnotes (5)

F1. Restricted stock units convert into common stock on a one-for-one basis.
F2. Shares withheld for payment of taxes upon vesting of restricted stock unit awards.
F3. On June 20, 2022, the reporting person was granted 434 restricted stock units, vesting in four equal annual installments beginning on the first anniversary of the grant date.
F4. On June 22, 2023, the reporting person was granted 693 restricted stock units, vesting in four equal annual installments beginning on the first anniversary of the grant date.
F5. Includes 100,003 shares of common stock underlying Series E warrants to purchase common stock.

Key Figures

RSU conversions: 283 shares Tax-withholding shares: 72 shares Post-transaction common shares: 12,381 shares +5 more

8 metrics

RSU conversions 283 shares Restricted stock units converted into common stock on June 20 and 22, 2026

Tax-withholding shares 72 shares Shares delivered to cover tax obligations at $2.88 and $3.12 per share

Post-transaction common shares 12,381 shares Common stock directly held by CFO following June 22, 2026 transactions

Post-transaction derivatives 147,718 securities Total derivative securities held after RSU conversions

Series E warrant underlying shares 100,003 shares Common stock underlying Series E warrants included in holdings

Tax-withholding price 1 $2.88/share Price used for 31-share tax-withholding disposition on June 20, 2026

Tax-withholding price 2 $3.12/share Price used for 41-share tax-withholding disposition on June 22, 2026

RSU grant 2023 693 RSUs Grant on June 22, 2023, vesting in four equal annual installments

Key Terms

Restricted stock units, tax-withholding disposition, derivative security, Series E warrants, +1 more

5 terms

Restricted stock units financial

"Restricted stock units convert into common stock on a one-for-one basis."

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

tax-withholding disposition financial

"Payment of exercise price or tax liability by delivering securities."

A tax-withholding disposition is an event or transaction—such as selling or transferring securities, exercising options, or receiving compensation—that triggers a requirement to hold back part of the payment and remit it to tax authorities. It matters to investors because it reduces the cash they receive immediately and can change the timing and amount of taxable income, like a cashier taking a portion of your sale proceeds to pay taxes before you get the rest.

derivative security financial

"Exercise or conversion of derivative security."

A derivative security is a financial contract whose value comes from the price or performance of something else, such as a stock, bond, commodity, or market index. For investors it acts like an insurance policy or a wager: it can be used to protect against losses, lock in prices, or amplify gains and losses, so it can change a portfolio’s risk and potential return without owning the underlying asset directly.

Series E warrants financial

"Includes 100,003 shares of common stock underlying Series E warrants to purchase common stock."

vests in four equal annual installments financial

"Vesting in four equal annual installments beginning on the first anniversary of the grant date."

FAQ

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

What insider transactions did Moleculin Biotech (MBRX) report for its CFO?

Moleculin Biotech CFO Jonathan P. Foster exercised restricted stock units and had shares withheld for taxes. In June 2026, 283 RSUs converted into common shares, while 72 shares were disposed of to satisfy tax obligations related to these vestings, rather than through open-market sales.

How many Moleculin Biotech (MBRX) shares did the CFO acquire and dispose of?

The CFO acquired 283 shares and disposed of 72 shares of Moleculin Biotech common stock. The 283 shares came from RSU conversions at $0.00 per share, while the 72 shares were withheld at $2.88 and $3.12 per share to cover tax liabilities on those awards.

What are Jonathan P. Foster’s holdings in Moleculin Biotech (MBRX) after these Form 4 transactions?

After the transactions, the CFO directly holds 12,381 shares of Moleculin Biotech common stock. He also holds 147,718 derivative securities, which the filing notes include 100,003 shares of common stock underlying Series E warrants, providing additional potential equity exposure.

Were Moleculin Biotech (MBRX) CFO’s Form 4 transactions open-market buys or sales?

The reported transactions were RSU conversions and tax-withholding dispositions, not open-market trades. Code M entries reflect derivative exercises at $0.00 per share, while code F entries show shares delivered to pay taxes on vesting, rather than discretionary market purchases or sales.

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

Form 4 Insider Transactions: What Each Field Means →

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Accepted by SEC EDGAR 06/24/2026 - 09:00 PM EDT

SEC Form 4

FORM 4

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

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Foster Jonathan P.

(Last)

(First)

(Middle)

C/O MOLECULIN BIOTECH, INC.

5300 MEMORIAL DR., SUITE 950

(Street)

HOUSTON

TEXAS

77007

(City)

(State)

(Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Moleculin Biotech, Inc. [ MBRX ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director	10% Owner
X	Officer (give title below)	Other (specify below)
	Chief Financial Officer

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
06/20/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	06/20/2026		M		109	A	⁽¹⁾	12,238	D
Common Stock	06/20/2026		F		31⁽²⁾	D	$2.88	12,207	D
Common Stock	06/22/2026		M		174	A	⁽¹⁾	12,381	D
Common Stock	06/22/2026		F		41⁽²⁾	D	$3.12	12,340	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
Restricted Stock Units	⁽¹⁾	06/20/2026		M			109	⁽³⁾	⁽³⁾	Common Stock	109	$0	147,892⁽⁵⁾	D
Restricted Stock Units	⁽¹⁾	06/22/2026		M			174	⁽⁴⁾	⁽⁴⁾	Common Stock	174	$0	147,718⁽⁵⁾	D

Explanation of Responses:

1. Restricted stock units convert into common stock on a one-for-one basis.

2. Shares withheld for payment of taxes upon vesting of restricted stock unit awards.

3. On June 20, 2022, the reporting person was granted 434 restricted stock units, vesting in four equal annual installments beginning on the first anniversary of the grant date.

4. On June 22, 2023, the reporting person was granted 693 restricted stock units, vesting in four equal annual installments beginning on the first anniversary of the grant date.

5. Includes 100,003 shares of common stock underlying Series E warrants to purchase common stock.

	/s/ Jonathan P. Foster	06/24/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)

Source: View Original Filing on SEC EDGAR