CN1C[C@H](C(=O)N[C@]2(C)O[C@@]3(O)[C@@H]4CCCN4C(=O)[C@H](Cc4ccccc4)N3C2=O)CC2c3cccc4[nH]cc(c34)C[C@H]21.O=C(O)C(O)C(O)C(=O)O
A higher pKa value denotes a less powerful acid. What is this molecule's pka value?