We examine SU(3) constraints on the spectrum and decay widths of cryptoexotic nucleon-like states in antidecuplet of pentaquarks. We show that in the ideal mixing scenario the number of free matrix elements describing splittings reduces from 4 to 2. Model-independent sum rules are derived. Using as input Θ+ and Ξ3/2 masses we show that it is difficult to interpret Roper and N*(1710) nucleon resonances as cryptoexotic pentaquarks. Large Nc limit for antidecuplet and accompanying octet in the diqaurk picture and the analogy with the soliton model is also discussed.