Polin succeeded ambassador Antoine de Rincon  in Constantinople. In early 1542, Polin successfully negotiated the details of a Franco-Ottoman alliance for the Italian War of 1542-1546, with the Ottoman Empire promising to send 27,500 troops against the territories of the Spanish king Ferdinand, as well as 110 galleys against Charles, while France promised to attack Flanders, harass the coasts of Spain with a naval force, and send 40 galleys to assist the Turks for operations in the Levant. Polin tried to convince Venice to join the alliance, but in vain. The execution of the alliance would most notably lead to the Franco-Ottoman Siege of Nice in 1543. In July 1543, Polin sailed on board the Ottoman fleet of Barbarossa to the Île Saint-Honorat in the Lérins Islands off Cannes on 5 July 1543, only to find very little ready for the offensive on the French side. Polin went to see king Francis I of France to obtain troops, which led to the Siege of Nice in August 1543. Polin supervised the wintering of the Ottomans at Toulon.. Who did not join the alliance?