(Updates with share performance)
SAO PAULO, Aug 7 (Reuters) - A minority investor in TPI Triunfo Participações & Investimentos SA asked Brazilian regulators on Monday to investigate whether state development bank BNDES' investment arm BNDESPar used privileged information to sell the infrastructure company's shares before an out-of-court debt restructuring.
In a letter seen by Reuters, investor Christian Bojlesen told securities industry watchdog CVM that BNDESPar, formerly Triunfo's No. 2 shareholder, might have sold the company's stock earlier this year to avoid being dragged into the out-of-court workout last month.
The letter said BNDES, with a representative installed in Triunfo's board, allegedly began proceedings to foreclose on collateral for two overdue Triunfo loans in January and February. It might have started to sell Triunfo shares once management and board members began to discuss the possibility of a workout, Bojlesen said.
BNDESPar and BNDES did not immediately comment on the letter. Triunfo declined to comment.
Between April and July, BNDESPar, whose complete name is BNDES Participações SA, cut its Triunfo stake to 5.1 percent from 14.8 percent, helping drive the stock down 41 percent.
The option to seek the workout, known as recuperação extrajudicial in Brazil, "was only made known to the public on July 23," when Triunfo reached a restructuring deal with lenders other than BNDES, he said.
The restructuring stems from Triunfo's default on an 800 million-real ($256 million) loan late last year.
Triunfo shares fell 3.5 percent on Monday to 3.61 reais, paring back gains this year to 13.9 percent. Benchmark Bovespa index was up 1.6 percent in mid-afternoon trading in Sao Paulo.
On July 22, a dozen banks joined a workout to restructure 2.1 billion reais of Triunfo's debt, giving the company a lifeline to complete projects and downsize gradually. BNDES, Brazil's main source of long-term corporate credit, did not participate in the workout.
Triunfo borrowed aggressively at the start of the decade to fund expansion in toll roads, electricity and airports. Brazil's worst-ever recession has eroded the company's profitability, and about 1 billion real of Triunfo's debt will mature by the end of next year.
Reuters reported on June 19, before the company disclosed a workout was under consideration, that it was close to a restructuring deal.
Last week, BNDES and BNDESPar filed a lawsuit to suspend Triunfo's workout and continue proceedings to foreclose on collateral for the defaulted loans. It accused Triunfo of misstating the size of BNDESPar's stake when announcing the workout.
Triunfo has five days to respond to BNDES' claims in court.
($1 = 3.1230 reais) (Reporting by Guillermo Parra-Bernal; Editing by Lisa Von Ahn and Phil Berlowitz)