Sotheby's has unveiled in London the Blaquier-Arrieta Collection, a group of 12 impressionist and post-impressionist paintings that will headline its November 18 evening sale in New York. The group is expected to fetch around $450 million, among the most valuable private collections ever offered at auction. The sale is led by two paintings that could set artist records. Vincent van Gogh's Chataignier en fleurs roses et blanches, painted in May 1890 shortly after the artist left the Saint-Remy hospital for Auvers-sur-Oise, is estimated at around $180 million, which would be a record for a Van Gogh at auction. Paul Cezanne's Arlequin carries an estimate of about $120 million; it is one of only two paintings from the artist's sequence of 15 late figure paintings still in private hands. Beyond the two headliners, Pierre-Auguste Renoir's En Canot (Jeune fille a la barque) is estimated at $25 to 30 million, Camille Pissarro's Parisian streetscape La Place du Theatre-Francais, soleil d'apres-midi en hiver at $30 to 40 million, and Edgar Degas' pastel Avant la course at $20 to 30 million. None of the three has previously been offered at auction. The group is completed by Monet's Le Jardin des Tuileries, Sisley's La Seine a Port-Marly, a rare Gauguin still life from his final years in Tahiti, a Toulouse-Lautrec portrait and two Fauve works by Derain and Vlaminck. The collection was assembled largely in the 1970s by the Argentine collectors Carlos Pedro Blaquier and Nelly Blaquier de Arrieta, with seven of the works, including the Cezanne, Renoir, Pissarro, Degas and Gauguin, acquired from the Lefevre Gallery on Bruton Street. The pictures were never lent to exhibitions and were known only through catalogue raisonnes, earning the collection the nickname of the El Dorado of South America. Philip Hook, the art historian and author, called it a miniature Musee d'Orsay now opening its doors for the first time.