Since joining the board of the Solomon R. Guggenheim Foundation three years ago, Janna Bullock, a Russian-born real estate developer, has been a frequent and glamorous presence on the circuit of art fairs, galas and biennials. She has sponsored art exhibitions in Venice and Miami, socialized with artists and collectors and even taken a motorcycle trip from St. Petersburg to Moscow with the actors Dennis Hopper and Jeremy Irons and Thomas Krens, the former Guggenheim director.


Janna Bullock and her husband, Aleksei Kuznetsov, at a 2007 gala.

But two weeks ago, Ms. Bullock abruptly left the board of the foundation, which oversees the Guggenheim Museum in New York and its satellites abroad. Her lawyer said she was taking a leave of absence to deal with a nasty business dispute in Russia — a conflict involving her husband, who was once a regional finance official there, and a company connected to Prime Minister Vladimir V. Putin’s former judo coach.

The lawyer, Robert Wolf, said Ms. Bullock wanted to defend herself against a “a malicious, vindictive and defamatory” media campaign in Russia that has resulted from the dispute.

The president of the Guggenheim, Jennifer Blei Stockman, confirmed that the board had granted Ms. Bullock a leave for personal reasons. “Clearly it’s a very difficult time that she’s going through,” she said. “We didn’t get into any of the gossip or the allegations,” she said, adding that “we have no idea what’s true or false.”

Ms. Bullock’s departure from the Guggenheim board is the latest twist in an operatic life. An immigrant from St. Petersburg, she worked as a nanny in Brooklyn before starting a New York real estate business. She expanded the business, turning it into what she described as a $2 billion company, by developing malls and summer homes near Moscow.

She met her husband, Aleksei Kuznetsov, who was then an executive at a Moscow bank, in 1994, while he was visiting New York. (In the years since, she has lived in New York, where she has a penthouse apartment on East 87th Street, and in Russia. He lived in Russia until 2008 and now lives in France.)

Ms. Bullock started her company, RIGroup, in 1998. Beginning in 2005, she began buying, renovating and selling Upper East Side town houses, many of them with storied or just plain strange pasts: Among her first purchases was 54 East 64th Street, The New York Observer building. In 2007, she bought the hole on East 62nd Street that was left after an Upper East Side doctor blew up his town house (and himself) to prevent his ex-wife from getting it.

Mr. Kuznetsov, meanwhile, became the finance director for the Moscow region in 2000. Three years later, Ms. Bullock made her expansion to Russia, acquiring vast tracts of land around Moscow to develop malls and homes, and eventually forming a partnership with a government corporation managed by her husband’s department.

In an interview in January, Ms. Bullock told The New York Times that, at the market’s peak, the company was worth $2 billion. The couple’s fortunes began to change in 2008. In July of that year, Mr. Kuznetsov resigned his government position and left Russia.

Mr. Kuznetsov said, in a separate interview in January, that he was pressured by a superior to resign because federal auditors were investigating Ms. Bullock’s company. After resigning, he went on vacation, and while he was gone, a political ally was shot in an apparent contract murder. Mr. Kuznetsov decided not to return to Russia, he said.

When Mr. Kuznetsov left his position, Ms. Bullock’s company in Russia was taken over by a rival company called ORSI, which has close Kremlin connections, as 25 percent of it is owned by a bank belonging to Mr. Putin’s former judo coach.

Ms. Bullock described ORSI as corporate raiders. “The moment my husband was kicked out of office, I had no control over my companies,” she said.

Representatives of ORSI said the company had been appointed by a court as a bankruptcy receiver for her properties and accused the couple of corruption and Ms. Bullock of profiting from her husband’s position. Recent articles in Russian newspapers have echoed these claims, which Ms. Bullock and Mr. Kuznetsov have denied.

Mr. Wolf said in a letter to The Times that journalists had “been offered money to print false stories” about Ms. Bullock. “Such blatant corruption,” he wrote, made the stories “highly suspicious at best.”

The Guggenheim was the first among New York museums to seriously cultivate relationships with rich Russian collectors, beginning in 2002 with the election to the board of the businessman Vladimir Potanin, and continuing with its 2005 exhibition “Russia!” for which Ms. Bullock helped raise money.

But Ms. Bullock’s sudden withdrawal may be a reminder to the museum of the risks of relying too much on Russian fortunes — what Mr. Wolf called, in another context, “the danger of doing business” there.