CAPR SPEC

Item 1.01. Entry Into A Material Definitive Agreement.

Amendment to Business Combination Agreement

As previously disclosed, on July 19, 2021, Capstar Special Purpose Acquisition
Corp., a Delaware corporation (the "Company"), entered into a Business
Combination Agreement (as amended by the Amendment to Business Combination
Agreement, dated as of November 8, 2021, the "Original Business Combination
Agreement"), by and among the Company, CPSR Gelesis Merger Sub, Inc., a Delaware
corporation and a wholly owned subsidiary of CPSR ("Merger Sub") and
Gelesis, Inc., a Delaware corporation ("Gelesis") that, among other things,
provides for Merger Sub to merge with and into Gelesis, with Gelesis as the
surviving company in the merger and, after giving effect to such merger, Gelesis
to be a wholly-owned subsidiary of the Company (the "Merger").

On December 30, 2021, the Company, Merger Sub and Gelesis entered into a Second
Amendment to the Original Business Combination Agreement (the "Second Amendment
to Business Combination Agreement", and together with the Original Business
Combination Agreement, the "Business Combination Agreement"), which, among other
things, removed the provisions relating to the issuance of 1,983,750 additional
Capstar Class A Shares to Gelesis stockholders, equal to the number of Capstar
Class B Shares forfeited by Capstar Sponsor Group LLC, a Delaware limited
liability company (the "Sponsor"), and certain affiliates of the Sponsor in
accordance with the Amendment to Sponsor Letter Agreement entered into by
Capstar, the Sponsor, certain affiliates of the Sponsor and Gelesis on November
8, 2021.

The Second Amendment to Business Combination Agreement is filed as Exhibit 2.1
to this Current Report on Form 8-K and the foregoing description is qualified in
its entirety by reference to the full text of the Second Amendment to Business
Combination Agreement.

Backstop Agreement

Pursuant to the Business Combination Agreement, the obligations of the parties
to consummate the Merger are subject to the satisfaction or waiver of certain
customary closing conditions of the respective parties, including, among other
closing conditions, that the Company's total available cash at the Effective
Time, after giving effect to (i) the $90.0 million PIPE Financing and (ii) the
Capstar Stockholder Redemptions, must not be less than $105 million (the
"Minimum Cash Condition").

In connection, and concurrently, with the execution of the Second Amendment to
Business Combination Agreement, on December 30, 2021, the Company entered into a
Backstop Agreement (the "Backstop Agreement") with PureTech Health LLC
("PureTech") and SSD2, LLC ("SSD2" and together with PureTech, the
"Purchasers"), pursuant to which the Purchasers agreed to purchase an aggregate
of up to 1,500,000 Capstar Class A Shares immediately prior to the Closing at a
cash purchase price of $10.00 per share (the "Backstop Purchase Shares"),
resulting in aggregate proceeds of up to $15.0 million, which amount, when added
to the proceeds from the PIPE Financing, is expected to ensure that the Minimum
Cash Condition will be satisfied. The Purchasers will only be obligated to
purchase Backstop Purchase Shares if, at the Effective Time, the amount of funds
remaining in the Trust Account after giving effect to the Capstar Stockholder
Redemptions (the "Available Funds") is less than $15.0 million, in which case
the Purchasers will purchase such number of Backstop Purchase Shares which
results in gross proceeds to the Company equal to the amount by which $15.0
million exceeds the Available Funds, subject to the other terms and conditions
of the Backstop Agreement. In addition, subject to the terms and conditions of
the Backstop Agreement and the terms and conditions of the Sponsor Letter
Agreement, at the closing of the sale of the Backstop Purchase Shares, the
Company will issue to the Purchasers 1,983,750 Capstar Class A Shares.

The Backstop Agreement contains customary representations, warranties, covenants
and agreements of the Company and the Purchasers and is subject to customary
closing conditions and termination rights. If the conditions to the consummation
of the backstop subscription contemplated by the Backstop Agreement are
triggered, the closing of the sale of the Backstop Purchase Shares is expected
to occur substantially concurrently with the Closing of the transactions
contemplated by the Business Combination Agreement.

Capitalized terms used but not otherwise defined in this Current Report on Form
8-K have the meanings given to such terms in the Business Combination Agreement.

The Backstop Agreement is filed as Exhibit 10.1 to this Current Report on
Form 8-K and the foregoing description is qualified in its entirety by reference
to the full text of the Backstop Agreement.

Item 3.02. Unregistered Sales of Equity Securities.

The disclosure set forth above in Item 1.01 of this Current Report on Form 8-K
is incorporated by reference herein. The Capstar Class A Shares to be offered
and sold and issued in connection with the Backstop Agreement will not be
registered under the Securities Act in reliance upon the exemption provided in
Section 4(a)(2) thereof.

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