The use of multicomponent reactions in the development of bis-boronic acids for the detection of β-sialic acid

Sialic acid (SA) is a naturally occurring monosaccharide found in glycoproteins and glycolipids. Changes in the expression of SA are associated with several diseases; thus, the detection of SA is of great significance for biological research, cancer diagnosis, and treatment. Boronic acid analogs have emerged as a promising tool for detecting sugars such as SA due to its reversible covalent bonding ability. In this study, 11 bis-boronic acid compounds and 2 mono-boronic acid compounds were synthesized via a highly efficient Ugi-4CR strategy. The synthesized compounds were subjected to affinity fluorescence binding experiments to evaluate their binding capability to SA. Compound A1 was shown to have a promising binding constant of 2602 ± 100 M-1 at pH = 6.0. Density Functional Theory (DFT) calculations examining the binding modes between A1 and SA indicated that the position of the boronic acid functional group was strongly correlated with its interaction with SA's α-hydroxy acid unit. The DFT calculations were consistent with the observations from the fluorescence experiments, demonstrating that the number and relative positions of the boronic acid functional groups are critical factors in enhancing the binding affinity to SA. DFT calculations of both S and R configuration of A1 indicated that the effect of the S/R configuration of A1 on its binding with β-sialic acid was insignificant as the Ugi-4CR generated racemic products. A fluorine atom was incorporated into the R2 substituent of A1 as an electron-withdrawing group to produce A5, which possessed a significantly higher capability to bind to SA (Keq = 7015 ± 5 M-1 at pH = 6.0). Finally, A1 and A5 were shown to possess exceptional binding selectivity toward β-sialic acid under pH of 6.0 and 6.5 while preferring to bind with glucose, fructose, and galactose under pH of 7.0 and 7.5.

[Full-thickness advancement flap of cheek with muscular pedicle in repair of defect of lips]

This paper reports a new technique to repair defects of the lip. It has been done in nine patients (2 upper lips and 7 lower lips), and the resultant oral configuration and function are satisfactory. The design and procedure are described in detail. The advantage of the method, the point for attention in performing the operation, and some problems in the repair of vermilion are discussed.

Clinical application of autogenous mandibular bone grafts. Analysis of 166 cases

Of the 166 patients receiving autogenous mandibular bone grafts during 1972-1987, 55 were used for repair of mandibular bone defect, 67 for correction of maxillofacial malformation and 44 for reconstruction of temporo-mandibular joint. Follow-up showed that 155 patients had satisfactory results after operation.

Rat brain hexokinase: the hydrophobic N-terminus of the mitochondrially bound enzyme is inserted in the lipid bilayer

Mitochondrially bound rat brain hexokinase was labeled with the photoactivatable reagent, 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine. This highly hydrophobic reagent is strongly partitioned into the hydrophobic environment of the membrane core, and thus selectively labels segments of a protein that penetrate this region of the membrane. Labeling of hexokinase was shown to be restricted to the N-terminal region of the molecule. Approximately 80% of the radiolabel was removed by treatment of the enzyme with chymotrypsin, which preferentially cleaves a hydrophobic 9-residue sequence at the extreme N-terminus of the enzyme, and it is considered likely that the remaining 20% was associated with two additional hydrophobic residues, immediately adjacent to this segment but not susceptible to cleavage by chymotrypsin. Labeling of the enzyme was shown to be dependent on maintenance of the association with the membrane. These results are consistent with a model in which binding of hexokinase involves insertion of an 11-residue hydrophobic N-terminal "tail," possibly existing in alpha-helical secondary structure, into the hydrophobic core of the membrane.