5 Channel Center South Boston. Courtesy photo

San Diego-based life science developer Phase 3 Real Estate Partners has acquired a pair of properties in Watertown and South Boston for $81.2 million.

5 Channel Center, a 52,000-square-foot office building, sold for $35 million and will be converted into 8,000-square-foot life science spec suites and branded as Genesis 5 Channel Center, according to Phase 3’s web site. In a separate transaction, Phase 3 acquired an office-lab development site at 85 Walnut St. in Watertown for $46.2 million, according to a deed filed in Middlesex County.

Westbrook Partners was the seller in both transactions. In July, Westbrook received approval for construction of the new 215,000-square-foot lab-ready building at 85 Walnut St. in Watertown, a 5-acre property that previously was headquarters of Doble Engineering.

Phase 3 Real Estate Partners’ existing local holdings include 1560 Trapelo Road in Waltham, which it acquired in January 2020 for $22.85 million. Dyne Therapeutics signed a full-building lease for 68,000 square feet in December, according to a Middlesex County Registry of Deeds filing.

Founded in 2000, Phase 3 has developed industrial, tech and life science properties and currently owns properties in San Diego and the San Francisco Bay area along with Greater Boston.