Partha Chattopadhyay

A GREEN CHEMICAL APPROACH FOR THE N-ALKYLATION OF ALDOXIMES TO FORM NITRONES IN ORGANIZED AQUEOUS MEDIA AND THEIR IN SITU CYCLOADDITION WITH OLEFINS

Aldoximes react with α,β-unsaturated carbonyl and sulfonyl compounds in organized aqueous media (nanoreactor system) using dodecylbenzenesulfonic acid (DBSA) as surfactant to generate N-alkylated nitrones, which undergo intermolecular cycloaddition in the same pot with maleimides to give the desired cycloadduct in absence of any organic solvent and catalyst. Divinyl sulfone was successfully used for both N-alkylation and intramolecular cycloaddition, affording only one cycloadduct. This is a new example of green chemistry and provides a new aspect of reactions in water.

Simultaneous Parallel and Antiparallel Self-Assembly in a Triazole/Amide Macrocycle Conformationally Homologous to d-,l-α-Amino Acid Based Cyclic Peptides: NMR and Molecular Modeling Study

A 1,4-linked triazole/amide based peptidomimetic macrocycle, synthesized from a triazole amide oligomer of cis-furanoid sugar triazole amino acids, possesses a conformation resembling the D-,L-α-amino acid based cyclic peptides despite having uniform backbone chirality. It undergoes a unique mode of self-assembly through an antiparallel backbone to backbone intermolecular H-bonding involving amide NH and triazole N2/N3 as well as parallel stacking via amide NH and carbonyl oxygen H-bonding, leading to the formation of a tubular nanostructure.

Synthesis of chiral trans-fused pyrano[3,2-c][2]benzoxocines from D-mannose by regioselective 8-endo-aryl radical cyclization

Abstract A simple chiral synthesis of trans -pyrano[3,2- c ][2]benzoxocines 8a – d in good yields (60–75%) through regioselective 8- endo - trig aryl radical cyclization of the d -mannose derived enopyranosides 7a – d with Bu 3 SnH is described.

Synthesis of chiral oxepanes and pyrans by 3-O-allylcarbohydrate nitrone cycloaddition (3-OACNC)

3-O-Allylcarbohydrate nitrone cycloaddition (3-OACNC) furnished pyran and oxepane derivatives from 3-O-allyl hexose N-benzyl nitrones and 3-O-allyl furanoside-5-aldehyde N-benzyl/methyl nitrones. The regioselectivity of 3-OACNC was found to depend on the following factors (a) the structural nature of the nitrone (b) substitution and stereochemistry at 3-C of the carbohydrate backbone (c) substitution at the terminus of the O-allyl moiety. Oxepanes or pyrans obtained from a particular set of a hexose nitrone and the corresponding furanoside nitrone were converted to enantiomeric cyclic ethers through degradation. A mixture of an oxepane and a pyran was formed in the intramolecular oxime olefin cycloaddition (IOOC) of a 3-O-allylcarbohydrate derived oxime.

An expeditious enantiodivergent synthesis of chiral oxepanes from D-glucose by the application of intramolecular 1,3-dipolar nitrone cycloaddition

Abstract The enantiomers of an oxepanoisoxazolidine and a chiral oxepane, potentially useful as precursors for naturally occurring oxepanes, were synthesised from D-glucose involving intramolecular 1,3-dipolar nitrone cycloaddition.

Synthesis and biological evaluation of dibenz[b,f][1,5]oxazocine derivatives for agonist activity at κ-opioid receptor.

A short and high yield synthetic route to dibenz[b,f][1,5]oxazocines has been developed using Pd catalyzed intramolecular cycloamination reaction. Receptor binding assay using [125I]-dynorphin demonstrated that one of the derivative, 5b showed selective κ-opioidergic property.

An alternative to ‘propylene/Leonard linker’ for studying arene interactions in flexible pyrazolo[3,4-d]pyrimidine core based models both at molecular and supramolecular levels

An alternative C-3 linker to ‘propylene/Leonard linker’ is proposed for studying arene interactions in face-to-face (offset) mode. The two new flexible symmetrical compounds with an electron deficient pyrazolo[3,4-d]pyrimidine core and biologically important isomeric purine systems and one dissymmetrical compound with a pyrazolo[3,4-d]pyrimidine core and electron-rich carbazole residue at the termini of the new linker show folding due to intramolecular π–π interactions by both 1H NMR in solution and X-ray crystallography in the solid state. Surprisingly, the replacement of the 4-methylsulfanyl group of the dissymmetrical compound by an electron donating methoxy group shows open conformation in the solid state by X-ray crystallography. The fifth symmetrical compound with an electron-rich carbazole residue at the termini of new linker, however, shows the normally expected open conformation.

Rational Construction of Triazole/Urea Based Peptidomimetic Macrocycles as Pseudocyclo-β-peptides and Studies on Their Chirality Controlled Self-Assembly

A tandem macro-dimerization reaction via a Cu(I) catalyzed azide/alkyne cycloaddition reaction has been employed to construct triazole/urea based peptidomimetic macrocycles considered as pseudocyclo-β-peptides. Introduction of one particular chirality in the peptide backbone can alter the conformation as well as nature of self-assembly from cyclic D-,L-,α-peptide to cyclo-β-peptide. One of them (16a) forms antiparallel dimers while the other (16b) undergoes higher order aggregation to form a nanorod structure.

Design and synthesis of conformationally homogeneous pseudo cyclic peptides through amino acid insertion: investigations on their self assembly

Macrocyclic C2 symmetric peptides, containing bis furanoid triazole amino acids as di-β-peptides linked to a D-α-amino acid or a β-amino acid in each half, have been designed and synthesized. The D-α-amino acid derived product undergoes parallel homo-stacking in solution via amide NH and amide carbonyl oxygen H-bonding; such macrocycles may be used as model systems for artificial ion channels as their unidirectional assembly pattern attributes them with large dipole moments. In contrast, the β-amino acid based compound forms only a conformationally homogeneous cyclic peptide without undergoing self assembly.

Synthesis of Two LewisX Trisaccharides Using Regiospecific Glycosylation Reactions

Synthesis of two LewisX trisaccharides, namely, 2‐(trimethylsilyl)ethyl 2,3,4,6‐tetra‐O‐acetyl‐β‐D‐galactopyranosyl‐(1→4)‐6‐O‐benzyl‐2‐deoxy‐3‐O‐(2,3,4‐tri‐O‐benzyl‐α‐L‐fucopyranosyl)‐2‐phthalimido‐β‐D‐glucopyranoside and 2‐(trimethylsilyl)ethyl 2,3,4‐tri‐O‐acetyl‐6‐O‐t‐butyldiphenylsilyl‐β‐D‐galactopyranosyl‐(1→4)‐6‐O‐benzyl‐2‐deoxy‐3‐O‐(2,3,4‐tri‐O‐benzyl‐α‐L‐fucopyranosyl)‐2‐phthalimido‐β‐D‐glucopyranoside, has been achieved using a regiospecific glycosylation strategy under NIS‐TfOH activation. Two trisaccharides were prepared from monosaccharides without any protecting group manipulation.