Workers have begun peeling away decades of alterations in the former dining room of the historic Pioneer Building in downtown Tucson, in an effort to restore the space to its former glory.

Holualoa Cos., which bought the former hotel at 100 N. Stone Ave. in 2004, has teamed up with new tenant SinfoníaRx to restore the roughly 2,000-square-foot dining room of the old Pioneer Hotel.

Holualoa plans to restore the dining room to as close to original as possible, while following current building codes, said Perry Whitthorne, asset manager for the real-estate investment and development company.

SinfoníaRx, a medication-management spinoff of the University of Arizona College of Pharmacy, is currently housed downtown at 1 E. Toole Ave. It was acquired by a Philadelphia-area company, Tabula Rasa HealthCare Inc. in September but has retained its name and local operation.

The company will make the Pioneer Building its headquarters, using the dining room as a reception and meeting area with open, loft-style offices overlooking the room from the second floor, said Kevin Boesen, CEO of SinfoníaRx.

About 50 employees will move into the office spaces when they are finished in January, Boesen said Thursday during a media reception for the new space. The dining room renovation is expected to be completed in May.

“The idea is to keep it open,” Boesen said of the dining room space. “We’ll use it probably for events, as a centerpiece for some company meetings, and there may be an opportunity to host some city meetings and things like that as well.”

SinfoniaRx also plans to install a vintage hotel reception desk and borrow some antique pharmacy items from the History of Pharmacy Museum at the UA College of Pharmacy to create a display in a staircase leading to the upper floor, said Boesen, a 1996 graduate of the UA pharmacy school.

“For us, being part of Tucson, it’s such an important thing to keep our headquarters here,” he said. “We really want to create a lot of energy around being part of that community, and there are so many people in the Tucson community who remember this dining room being here. We wanted people to have that connection to Tucson and wanted the young people we hire to embrace that history as well.”

The original Pioneer Hotel, designed in a Spanish Revival style by Tucson architect Roy Place, opened in 1929 as one of Tucson’s first high-rise buildings and was a center of downtown life for decades until a 1970 fire that claimed 29 lives.

After the fire, the building was converted into offices and renovated in 1970s style on the exterior, while interior renovations over the years hid architectural features such as the dining room’s ornate, coffered ceiling.

Most recently, the dining room was used by the Tucson-Pima Arts Council and Startup Tucson, a non-profit entrepreneurship program that occupies an adjacent office.

Workers are in the process of stripping away years of renovation work, including wall additions, old wallpaper and dark-wood paneling, to uncover original designs.

The room’s molded plaster ceiling, which was covered by a suspended acoustic-tile ceiling that concealed modern ductwork, wiring and sprinkler plumbing, will be repaired in places where holes were punched during prior installations and in some cases new coffers, or recessed ceiling squares, will be made of molded fiberglass, Whitthorne said.

“One of our biggest challenges is to retain that historical look and feel as best we can, but there will be some modifications,” he said, citing required sprinklers and modern heating and air conditioning.

The company wants to restore the dining room’s original maple wood floor, which shows signs of termite damage, depending on its condition, Whitthorne said.

Features like column-like wall pilasters and decorative arches will be restored, and mechanical equipment will be relocated and hidden, he added.

The cost of the project will run into the “high six figures,” with Holualoa covering the cost of the upstairs office improvements and Holualoa and SinfoníaRx sharing the cost of the dining room renovation, Whitthorne said.

A local office of Milwaukee-based Engberg Anderson Design is handling the architectural design. The general contractor is Tucson-based MW Morrissey, working with local historic preservation specialist Oden Construction.

Contact senior reporter David Wichner at dwichner@tucson.com or 573-4181. On Twitter: @dwichner

Senior reporter covering business and technology for the Arizona Daily Star/Tucson.com