Salts of tryptophan with p-toluenesulphonic acid and camphorsulphonic acids

Abstract

Co-crystallisation of dl-tryptophan with p-toluenesulphonic acid, R-camphor-10-sulphonic acid and S-camphor-10-sulphonic acid resulted in salts. For all the structures, the amino acid is in the cationic form with the proton transferred from the acidic co-former to the amino acid. R-camphor-10-sulphonic acid and S-camphor-10-sulphonic acid were unsuccessful at resolving dl-tryptophan. Dissolution of the respective camphorsulphonic acid and dl-tryptophan in methanol/water gave crystals which contained equimolar amounts of the d- and the l-tryptophan. The following salts were also obtained in aqueous acetonitrile; (2l-TRP+)(2S-CSA−)·(H2O) from a mixture of l-TRP/S-CSA and (d-TRP+)(S-CSA−) from a mixture of d-TRP/S-CSA. The crystal structures and the thermal stability of the salts have been determined. (dl-TRP+)(p-TSA−) solved in P21/c with a = 19.422(2) Å, b = 5.5456(7) Å, c = 16.488(2) Å and β = 102.357(2)°. (d-TRP+)(l-TRP+)(2R-CSA−) solved in P21 with a = 12.780(3) Å, b = 10.411(2) Å, c = 32.574(7) Å and β = 97.60(3)°. (d-TRP+)(l-TRP+)(2S-CSA−) solved in P21 with a = 12.783(3) Å, b = 10.410(2) Å, c = 32.564(7) Å and β = 97.44(3)°. (2l-TRP+)(2S-CSA−)·(H2O) solved in P21 with a = 13.1761(12) Å, b = 10.3092(10) Å, c = 16.6268(16) Å and β = 104.435(2)°. (d-TRP+)(S-CSA−) solved in P212121 with a = 6.4185(13) Å, b = 12.700(3) Å, c = 25.173(5) Å and α = β = γ = 90°.