Valerian T. D'Souza

A convenient method for functionalization of the 2-position of cyclodextrins

Abstract A new convenient strategy for functionalization of the 2-position of cyclodextrins involving deprotonation of cyclodextrin by sodium hydride followed by a nucleophilic attack of the resultant cyclodextrin oxyanion on the desired electrophile gives a high yield of the cyclodextrin derivative.

Selective modification at the 3-position of β-cyclodextrin

Abstract Heptakis(6- O - tert -butyldimethylsilyl) β -cyclodextrin reacts with N -methyl-4-chloromethyl-2-nitroaniline to produce the 3-modified cyclodextrin after the necessary deprotection step. Complete NMR assignment and its comparison with cyclodextrin derivatives modified by the same group at the 2- and 6-position is reported.

Influence of Positively-Charged Guests on the Superoxide Dismutase Mimetic Activity of Copper(II) β-Cyclodextrin Dithiocarbamates 1

Abstract The superoxide dismutase (SOD) activity of the Cu(II) complexes of two dithiocarbamate derivatives of cyclodextrin (Cu-C6DTC, Cu-C2DTC), one on the primary (C6DTC) and the other on the secondary (C2DTC) side, was determined in the presence of positively-charged guests which have the general formula RNX3 + (where R = C6H11, X = CH3 (3); R = C6H11, X = C2H5 (4); R = p-CH3C6H4, X = CH3 (5) and R = p-CH3C6H4, X = C2H5 (6). The catalytic activity of both Cu-C2DTC. and Cu-C6DTC was enhanced 35–70% by 3–6 for concentrations of the host equivalent to the IC50 value of the complex. A correlation was found between the net positive charge of the nitrogen atom and the maximum acceleration attained by both complexes. The formation of an inclusion complex between these cationic guests and the CD moiety of these complexes is proposed to be the determining factor in the observed increase in the catalytic activity. 1. Part 2 of the series “Copper Complexes of Cyclodextrin Dithiocarbamates as Superoxide Dismutase ...

Electrophilic Catalysis by Cyclodextrins.

Abstract The catalysis of an aromatic electrophilic substitution reaction by cyclodextrins is reported. The catalysis can be explained on the bases of the electron rich character of the interior of the cyclodextrin cavity. Kinetic analyses of this reaction in the presence of cyclodextrins indicate binding and catalysis.

Selective protection of the secondary side of β-cyclodextrin

Abstract Selective protection of the secondary side of β-cyclodextrin by reaction with t -butyldimethylsilyl chloride in the presence of NaH in dry DMF, is reported. Although, all the hydroxyl groups are not silylated in this reaction, these groups offer steric protection and direct the incoming electrophile to the primary side of the molecule.

An NMR approach for the determination of the substitution pattern in mono-modified cyclodextrins

Abstract One of the problems in cyclodextrin chemistry is the unequivocal determination of structures of systems under investigation. A simple procedure that can be used for the determination of the position of the substitution in these systems is presented here. The main requirement of this procedure is that the proton attached to the substituted carbon has a magnetic environment that is different from other likely sites of attachment.

Self assembly in custom designed cyclodextrins

Abstract Synthesis of the first custom designed cyclodextrins obtained by a nucleophilic attack on hepatkis-2,3-epoxy-β-cyclodextrin is reported. This novel cyclodextrin provides amine functionalities in addition to hydroxyl groups for chemical processes. Spectral evidence shows that the cavity in this new cyclodextrin is flexible and it self assembles into a dimer under specific conditions.

Flavocyclodextrins as artificial redox enzymes. Part 4. Catalytic reactions of alcohols, aldehydes and thiols

The catalytic reactions of models of flavoenzymes in which flavin is covalently attached to the catalytically important secondary side of cyclodextrin 2-[(7α-O-10-methyl-7-isoalloxazino)methyl]-α-cyclodextrin and 2-[(7α-O-10-methyl-7-isoalloxazino)methyl]-β-cyclodextrin are reported.

Application of a selective HSQC experiment to measure interglycosidic heteronuclear long-range coupling constants in cyclodextrins

A selective one‐dimensional HSQC experiment was used to obtain heteronuclear long‐range coupling constants for native and chemically modified cyclodextrins (3,6‐anhydro‐β‐cyclodextrin) and a non‐covalent complex of α‐cyclodextrin with p‐nitrophenol. Selective excitation was performed on C‐4 in the α‐glucose units using DANTE hard pulse trains. The measured heteronuclear long‐range coupling constants have similar values for all natural cyclodextrins. The high value of these coupling constants indicates that the low dihedral angle between H‐1 and C‐4 found in the solid state is retained in solution. Chemical modification or complex formation, however, decreases the coupling constant by increasing the dihedral angle between these nuclei.

Accelerated Transacylation of Unactivated Phenyl Esters at Physiological pH with β-Cycloaltramine

Abstract The recently reported novel cyclodextrin, β-cycloaltramine, exhibits a 5.3 × 104 fold acceleration (compared to buffer) in transacylation of unactivated phenyl esters at physiological pH and follows saturation kinetics similar to enzymes. This acceleration is attributed to the change of the nucleophile and better binding of the substrate by this novel flexible host.