Answer
The answer is Leonardo da Vinci. Although Alkan met and befriended many notable figures, including artists such as Corot and Delacroix, and composers like Rossini, Cherubini, and Liszt, Leonardo da Vinci was not among his acquaintances. Alkan's circle primarily comprised individuals from the world of music and arts during his era, rather than figures from the Renaissance period like Leonardo da Vinci.