Sunovion Pharmaceuticals Inc, the Marlborough-based subsidiary of a big Japanese drug company, said Thursday that it has agreed to buy Elevation Pharmaceuticals Inc., a privately held company specializing in the development of aerosol therapies for patients with respiratory diseases.

Sunovion said it will make an upfront payment of $100 million to the shareholders of California-based Elevation on the closing of the acquisition.

The sales agreement also calls for development milestone payments of up to $90 million if an Elevation Pharmaceuticals drug candidate achieves certain goals. If the drug candidate gets regulatory approval, Sunovion said it could make commercial milestone payments of up to $210 million. Subsequent milestone payments up to $30 million could occur contingent upon the successive development of additional new programs.

An Elevate drug candidate referenced in the sales agreement is designated as EP-101; it is an inhalation solution that is being developed as a potential treatment for patients with moderate to severe chronic obstructive pulmonary disease, or COPD.

Until a few years ago, Sunovion was known as Sepracor. One popular drug that Sepracor made is a sleep aid that is sold under the brand name of Lunesta.

In 2009, Sepracor was bought for $2.6 billion by Japanese drug maker Dainippon Sumitomo Pharma Co., which later changed Sepracor’s name to Sunovion.