Synthesis and carboxylate anion binding studies on cyclic sugar-amino acid hybrids

Abstract

Here in, the condensation of boc-glycine with 2,6-anhydro-3,4,5-tri-O-benzyl-D-gluco-heptitol followed by its boc-deprotection to form 2,6-anhydro-3,4,5-tri-O-benzyl-D-gluco-heptitolyl bis-glycinate, which in turn on condensation with succinic acid/pyridine-2,6-dicarboxylic acid led to the formation of sugar-amino acid hybrid macrocyclic compounds 4, 6 and debenzylated marocyclic compound 5, having amide bonds that function as efficient host for polar, hydrogen bond acceptors and carboxylate ions. The anion inclusion capability of synthesized macrocylic hosts has been evaluated by the study of their binding with boc-GlyCOOˉ anion as guest through 1H NMR titration studies in CDCl₃. The binding constant (K_a) of boc-GlyCOOˉ guest with macrocyclic hosts 4 and 6 involving succinate and pyridine-2,6-dicarboxylate linkers was found to be 9.201 × 10³ and 1.437 × 10⁴ M⁻¹, respectively. The higher binding constant was observed in the complex of boc-GlyCOOˉ with pyridine-dicarboxylate containing host may be due to the extra rigidity & suitable conformation attained by the presence of rigid-aromatic dicarboxylate linker.

Graphical Abstract

Keywords:

• Binding constant
• carboxylate ion
• glycine
• heptitol sugar
• NMR titration
• sugar-amino acid based macrocycle

Acknowledgements

AS, VKM and VV acknowledge financial support from DBT and CSIR for Research Associate and Junior/Senior Research Fellowship, respectively. The authors acknowledge CIF-USIC University of Delhi, Delhi for providing NMR, HRMS and other instrumentation facilities.

Additional information

Funding

The author would like to thank University of Delhi for financial assistances from DU-DST Purse Grant and DU R&D grant to strengthen research and development.