Peptide Side-Arm Derivatives of Lariat Ethers and Bibracchial Lariat Ethers: Syntheses, Cation Binding Properties, and Solid State Structural Data

Article abstract of DOI:10.1021/jo00265a038

Aza-18-crown-6 and 4,13-diaza-18-crown-6 derivatives having one or two side arms have been prepared.The side arms are of the form >N-Gly-AA-OMe, where "AA" is an amino acid.The 18-membered ring compounds were prepared by alkylation of aza-18-crown-6 as follows: Gly-Gly-OMe (14, 57percent, mp 42-43 deg C); Gly-Ile-OMe (15, 50percent); Gly-Val-OMe (16, 56percent).Two-armed compounds were obtained by alkylation of 4,13-diaza-18-crown-6 as follows: Gly-Gly-OMe (18, 58percent, mp 118-119 deg C); Gly-Ala-OMe (19, 50percent, mp 62-63 deg C); Gly-Phe-OMe (20, 65percent, oil); Gly-Leu-OMe (21, 51percent, mp 72-73 deg C); Gly-Ile-OMe (22, 60percent, oil); Gly-Val-OMe (23, 59percent, oil).Sodium iodide complexes of 18, 19, and 20 were isolated.Solid state structural data are reported for 18 and its sodium complex, as well as its potassium complex that was reported in preliminary form (ref 9f).Compound 18 crystallizes in the triclinic space group P1 with cell constants a = 9.0210 (8), b= 10.4768 (15), and c = 15.357 (2) Angstroem, α = 87.457 (12) deg, β = 87.119 (10) deg, γ = 68.042 (9) deg, and Z = 2 for D_c = 1.286 g cm^-3.Least-squares refinement based on 4034 observed reflections led to a final conventional R value of 0.041.The sodium iodide complex of 18 crystallizes in the monoclinic space group P2₁/c with cell constants a = 9.732 (3), b = 17.710 (2), and c = 38.848 (3) Angstroem, β = 96.99 (2) deg, and Z = 8 for D_c = 1.430 g cm^-3.Least-squares refinement based on 5512 observed reflection led to a final conventional R value of 0.041.The potassium iodide complex of 18 crystallizes in the monoclinic space group C2/c with cell constans a = 15.656 (4), b = 14.752 (3), and c = 26.784 (3) Angstroem, β = 90.01 (2), and Z = 8 for D_c = 1.474 g cm^-3.Least-squares refinement based on 2595 observed reflections led to a final conventional R value of 0.035.There are two crystallographically independent molecules in each of the three crystal structures.The sodium and potassium complexes are compared to other BiBLE complexes and to cryptates.Cation binding affinities for these compounds have been assessed in anhydrous methanol and are reported here for Na⁺ and K⁺ cations.