Three Columbus Circle is starting to get serious about dating a prospective tenant.

Ad giant WPP Group, which has been conducting a thorough search for around 350,000 square feet for its storied Y&R division through “Powerwoman” Mary Ann Tighe of CBRE, is now cuddling up to 3 Columbus in a long dance toward a possible and “complicated” lease.

The global company is already familiar with 3 Columbus Circle’s co-venturer, SL Green Realty Corp., which stepped in last year to pay off developer Joseph Moinian’s loans in return for a front seat at the deal table.

WPP, which also houses agencies JWT, Ogilvy & Mather and Grey, currently leases some 43,000 square feet at SLG’s 100 Park Ave., so it is familiar with the real-estate investment trust’s operations.

The company is not afraid to break ground or head for new horizons in return for branding opportunities.

In 2008, when space was tight, WPP’s Ogilvy & Mather signed a lease for a 564,363-square-foot headquarters in the converted warehouse at 636 Eleventh Ave. at West 47th Street, where they moved from Worldwide Plaza.

Tighe declined comment as did CBRE and SLG.

Last year, Moinian had deals lined up with the William Morris Agency for 77,000 square feet and HQ Global Workplaces for 33,000 square feet before he was taken to court by Related Cos. in a foreclosure bid that was detoured by SLG’s participation and payoff.

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The five-story building at 309 Fifth Ave. is in contract to be sold to an entity controlled by the New Tower Trust Co. of Bethesda, Md.

The 27,000-square-foot building is actually a 150,000-square-foot development site being sold by an entity controlled by a fashion company and Urban Development Partners.

Sources said the site was last sold in 2006 for about $50 million and carried a $31 million mortgage from Arbor. The same garmentos turned over a $50 million building at 63 W. 38th St. to Savanna Partners last year.

No one returned calls for comment.

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New York Cares, the organization that trains 16,000 volunteers each year for 1,200 non-profits, will be moving downtown in an 11-year deal for 18,000 feet at the 21-story 65 Broadway. The firm currently occupies 11,198 square feet at 214 W. 29th St.

The new 19th floor space and a portion of another level will be entirely built out for the non-profit group, which will relocate this spring.

According to a report by the Downtown Alliance, 50 non-profits have moved downtown since 2005 due to lower rents, incentives and transportation.

Carri Lyon of Cushman & Wakefield represented the tenant, while the owners, A.M. Property, were repped by a C&W team led by Tom Kaufman and Rory Murphy.

The asking rent was in the low $30s a foot, and the group will also receive a downtown relocation benefit, Lyon said.

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Whiskey maker William Grant & Sons, which is also the distiller of the best-selling Glenfiddich, has signed a 10-year lease at 300 Park Ave. South. The new US headquarters is between E. 22nd and 23rd Streets. The company is currently located in 200 Park Ave. South.

In the new Rockrose Development Co.-owned building, William Grant will have over 20,000 square feet on the 5th and 6th floors.

Eric Cagner of Newmark Knight Frank represented the tenant in the transaction. Andrew Peretz, John Peters and Mikael Nahmias of Cushman and Wakefield negotiated on behalf of Rockrose, which had an asking rent of $51 a foot.

The tenant’s private dining area will also include a high-class bar in keeping with its history of selling fine liquors.

According to Craig Deitelzweig of Rockrose, the entrance to the building was moved, and the lobby is being expanded in a design by Moed de Armas & Shannon that will be completed next month.

Other newcomers to the building include Leo Burnett, the Whitney Museum, M. Booth, Rizzoli Publishing and Wilhelmina.

“We’ve signed 12 floors in the last year,” said Deitelzweig. “We had all of our spaces rolling at the same time but took the opportunity to reformulate the building and make it the premier building on Park Avenue South.”

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A group that has jailbirds train puppies as service dogs for disabled veteran service members has leased 5,000 square feet at 263 W. 38th St. Puppies Behind Bars will relocate from 10 E. 40th St. at the end of the year.

The non-profit has trained local inmates to teach the pups 90 commands over 22 months. The dog graduates are transferred free of charge to wounded service members with Post-Traumatic Stress Disorder and Traumatic Brain Injury.

Scott Galin and Peter Newman of Handler Real Estate Organization, represented Handler in-house as the building’s owner.

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