PORTSMOUTH — In a rapidly developing city, sibling developers Michael and John Kane are rapidly developing multiple Portsmouth properties.

They've partnered with the city to redevelop the Thomas J. McIntyre Federal Building property and signed a lease with McIntyre tenant, the Internal Revenue Service, to move into a new Kane building at 75 Portsmouth Blvd.

At the same time, the brothers have broken ground on 42 acres they own off Borthwick Avenue for a new 68,000-square-foot medical building, where there's room for more development. And on Wednesday night, the Kanes will present plans for a new 75,000-square-foot office building at the corner of Maplewood Avenue and Vaughan Street, now a construction-staging area for a new AC Hotel going up across the street.

The brothers said they bought the undeveloped land between Islington Street and Borthwick Avenue in 2006, where they first planned to develop a long-term care facility, similar to RiverWoods in Exeter. Michael Kane said they had city support until neighbors objected and after a third reading for those plans, the City Council failed to grant a needed zoning change.

John Kane said they were left with the original office-research zoning for the undeveloped property and began making plans, now coming to fruition, after city denials, then litigation. A Supreme Court appeal was dropped by agreement with the city and the brothers are now overseeing development of a 4-story medical building on the Borthwick Avenue land, with underground parking.

John Kane said they were initially contacted by a financial services company, for 100,000 square feet of space at the site, but they turned it down to "make our bet on medical."

The brothers said Tuesday they're in the midst of lease negotiations with a medical entity for half the building before the foundation is even poured. John Kane said the building is expected to be finished in "early 2020."

As demand grows, the brothers said, they expect to build more there.

"We could build four or five more of these," John Kane said at the site Tuesday.

Drawings for the new building are titled "Portsmouth Medical Park."

"We think it's the future of the medical expansion in Portsmouth," Michael Kane said.

A road is being built off Borthwick Avenue and will also allow for only emergency vehicles to access the site from Islington Street.

"If you were having a heart attack on Islington Street I bet you wish you could come through," Michael Kane said, from a spot with views of existing medical buildings on one side and Islington Street on the other.

The land is known locally as the location of the former WBBX radio station building. Railroad tracks cross the property and after some back-and-forth with the city about whether the Kanes would build a bridge over the tracks, or not, the final plans now call for a simple railroad crossing.

The brothers on Wednesday will present preliminary plans to the Historic District Commission for a 75,000-square-foot office building on the 111 Maplewood Ave. property where the Portsmouth Herald office was previously located, before a move to Pease International Tradeport. Michael Kane said they're already in serious negotiations with a tenant for that development, on property they have under agreement. His brother said they're negotiating with three potential tenants.

That building, as currently planned, would be 3˝ stories tall and L-shaped around the bend in Vaughan Street.

Michael Kane said Wednesday's HDC meeting will be to review the planned massing of that proposed office building, so the plans could change. After that, he said, they'll take it to the Technical Advisory Committee, then the Planning Board.

"Then," he said, "Add water, stir and be done."