Molecular structure of enzyme-synthesized amylose-like chimeric isomaltomegalosaccharides and their encapsulation of the sulfasalazine prodrug

The glucoconjugation between linear chimeric α-(1→4)- and α-(1→6)-glucosidic segments exhibits functional properties throughout their structure. In this study, we enzymatically synthesized three new series of chimeric nonreducing isomaltomegalosaccharides (N-IMS-n/m), each featuring a constant n, α-(1→4)-segment (average degree of polymerization, DP = 22–25) at the nonreducing terminal, and varying m, α-(1→6)-main chain lengths (DP = 7–53). The synthesized compounds—N-IMS-25/7, N-IMS-24/19, and N-IMS-22/53—were compared to amylose (DP = 28) and previous samples of N-IMS-15/35 and D-IMS-28.3/13/3. D-IMS refers to a sugar with double α-(1→4)-segments at both the nonreducing and reducing ends. The binding affinity to the aromatic prodrug sulfasalazine (SZ) was assessed using a phase-solubility assay, followed by freeze-thawing. Wide-angle X-ray scattering revealed B-type crystalline patterns in bulk, and the crystallinity generally reduced with the increasing α-(1→6) segment. Interestingly, the B-type crystal structure was maintained even after SZ encapsulation, in contrast to the more common transition to V-type crystals upon drug encapsulation. Multi-angle dynamic light scattering and small-angle X-ray scattering revealed an intricate solution-state morphology, both in the absence and presence of SZ. Glucoconjugation aids in maintaining structural organization and integrity, even after the incorporation of the large SZ molecule.