July 19 (Reuters) - PureTech Health-founded Gelesis will list on the New York Stock Exchange through a merger with an acquisition vehicle, valuing the weight management firm at about $1.3 billion, it said on Monday. Gelesis, founded by London-listed biotech firm PureTech, will merge with Capstar Special Purpose Acquisition Corp (SPAC), sponsored by affiliates of Capstar Partners LLC and funds managed by bond giant PIMCO. (Reporting by Indranil Sarkar in Bengaluru; Editing by Shailesh Kuber)