Mohan M. Bhadbhade

A new BIS-Andrographolide Ether from Andrographis paniculata Nees and evaluation of anti-HIV activity

Novel bis-andrographolide ether (1) and six known compounds andrographolide, 14-deoxy-11,12-didehydroandrographolide, andrograpanin, 14-deoxyandrographolide, (±)-5-hydroxy-7,8-dimethoxyflavanone, and 5-hydroxy-7,8-dimethoxyflavone have been isolated from the aerial parts of Andrographis paniculata and their structures were established by spectral data. All the isolates were tested for the anti-HIV and cytotoxic activity.

Crystal-to-crystal transformation amongst dimorphs of racemic 2,6-di-O-(p-halo benzoyl)-myo-inositol 1,3,5-orthoformates that achieves halogen bonding contacts

Racemic 2,6-di-O-(p-halobenzoyl)-myo-inositol 1,3,5-orthoformates (bromo (1) and chloro (2)) produced two polymorphs each, thin needle type crystals (Form I) were obtained from methanol, whereas larger rectangular crystals (Form II) were produced from ethyl acetate. Both forms could be produced concomitantly on crystallization (of 1 or 2) from ethyl acetate–light petroleum ether mixture; the yield of Form II crystal was always much more compared to Form I crystals. Although, a one-dimensional isostucturality linking molecules via O–H⋯O hydrogen bonding is seen in both forms, the difference arises in linking these chains. In larger Form II crystals (of 1 and 2), the adhesions are viahalogen bonding (C–X⋯OC, X = Cl, Br) contacts, whereas in smaller Form I crystals C–H⋯X contacts join them. Interestingly, DSC and X-ray crystallographic studies confirmed the thermal crystal-to-crystal transition of Form I to Form II crystals. Transformation of a minor to major polymorph containing ‘C–Br⋯OC’ contacts, similar to the phase transition previously reported by us in the case of 2,4,6-tri-O-(p-bromobenzoyl)-myo-inositol 1,3,5-orthoformate, suggests the role of X⋯O short contacts in preferential nucleation and crystal growth.

Enhancing Intermolecular Benzoyl‐Transfer Reactivity in Crystals by Growing a “Reactive” Metastable Polymorph by Using a Chiral Additive

Racemic 2,4-di-O-benzoyl-myo-inositol-1,3,5-orthoacetate, which normally crystallizes in a monoclinic form (form I, space group P2(1)/n) could be persuaded to crystallize out as a metastable polymorph (form II, space group C2/c) by using a small amount of either D- or L- 2,4-di-O-benzoyl-myo-inositol-1,3,5-orthoformate as an additive in the crystallization medium. The structurally similar enantiomeric additive was chosen by the scrutiny of previous experimental results on the crystallization of racemic 2,4-di-O-benzoyl-myo-inositol-1,3,5-orthoacetate. Form II crystals can be thermally transformed to form I crystals at about 145 degrees C. The relative organization of the molecules in these dimorphs vary slightly in terms of the helical assembly of molecules, that is, electrophile (El)...nucleophile (Nu) and C-H...pi interactions, but these minor variations have a profound effect on the facility and specificity of benzoyl-group-transfer reactivity in the two crystal forms. While form II crystals undergo a clean intermolecular benzoyl-group-transfer reaction, form I crystals are less reactive and undergo non-specific benzoyl-group transfer leading to a mixture of products. The role played by the additive in fine-tuning small changes that are required in the molecular packing opens up the possibility of creating new polymorphs that show varied physical and chemical properties. Crystals of D-2,6-di-O-benzoyl-myo-inositol-1,3,5-orthoformate (additive) did not show facile benzoyl-group-transfer reactivity (in contrast to the corresponding racemic compound) due to the lack of proper juxtaposition and assembly of molecules.

Capturing a metastable chiral polymorph of an achiral molecule--hexa-O-benzoyl-myo-inositol.

myo-Inositol hexabenzoate having meso configuration produces chiral polymorph (form I) when crystallized rapidly but yields achiral polymorph (form II) when allowed to crystallize slowly; in the mother liquor form I slowly but completely disappears to give form II.

Ferrocene-linked thymine/uracil conjugates: base pairing directed self-assembly and supramolecular packing.

Ferrocene-linked bis(nucleobase) (1a-c) and chimeric nucleobase (1d) conjugates have been synthesized from mono- and bis(hydroxybutyl)ferrocene 6 via Mitsunobu reaction as the key step. X-ray crystallographic studies of ferrocene bis(nucleobase) conjugates reveal two-dimensional supramolecular organizations of backbones through self-assembled Watson-Crick and reverse Watson-Crick type pairs. Ferrocene-bis(thymine) conjugate self-assembles by reverse Watson-Crick pairing, while the corresponding bis(uracil) conjugate self-assembles by alternating WC and reverse WC type pairing. Such continuous assemblies are not seen in monosubstituted ferrocene nucleobase conjugates which form only planar sheets. The results are interesting from the point of understanding and engineering supramolecular assemblies through rational design of base pairing patterns.

Ferrocene-bis(thymine/uracil) conjugates: base pairing directed, spacer dependent self-assembly and supramolecular packing.

X-ray crystallographic studies of methylene linked Ferrocene-bis(thymine/uracil) conjugates Fc(T:T)(M) and Fc(U:U)(M) reveal base dependent 2-D supramolecular assemblies generated via wobble self-pairing for bis-thymine and reverse wobble self-pairing for bis-uracil conjugates, differing in architecture from the corresponding butylene spacer linked conjugates.

Boronated phosphonium salts containing arylboronic acid, closo-carborane, or nido-carborane: synthesis, X-ray diffraction, in vitro cytotoxicity, and cellular uptake

The preparation of boronated triaryl and tetraaryl phosphonium salts of the type [PPh3CH2R]Br [Rxa0isxa04-boronophenyl (1), 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-yl)phenyl (2), 3-boronophenyl (3), 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-yl)phenyl (4), 2-boronophenyl (5), 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-yl)phenyl (6), and closo-1,2-carboran-1-yl (7)] is described. These compounds were prepared by the reaction of triphenylphosphine with benzylic bromides or 1-bromomethyl-closo-1,2-carborane in acetonitrile solution at 85xa0°C. The zwitterionic nido-7,8-carborane derivative PPh3CH2C2B9H11 (8) was prepared by treatment of 7 with cesium fluoride in refluxing ethanol. All compounds were fully characterized by multinuclear (1H, 11B, 13C, and 31P) 1D- and 2D-NMR spectroscopy, electrospray ionization mass spectrometry, and elemental analysis, and single-crystal X-ray structures were determined for compounds 1, 3, 7, and 8. The cytotoxicities and boron uptake of selected derivatives were investigated in vitro using human glioblastoma (T98G) and canine kidney tubule (MDCK II) cells. The zwitterionic species 8 was found to be the least cytotoxic agent while also delivering the greatest amount of boron to the T98G cells, peaking at 9.15xa0±xa02.65xa0μgxa0B/mg protein.

Isostructural molecular strings linked via conserved dipolar (ether) O⋯CO short contacts in conformational polymorphs of racemic 2,4-di-O-acetyl-6-O-tosyl-myo-inositol 1,3,5-orthoesters

Conformational dimorphs of racemic 2,4-di-O-acetyl-6-O-tosyl-myo-inositol 1,3,5-orthoformate and its orthoacetate analogue were characterized using single crystal X-ray diffraction, thermal analysis and hot-stage microscopy techniques. In these polymorphs, the tosyl group adopted different conformations due to the rotation about the O–S bond. A significant variation in the torsion angle for the tosyl group (∼56°) was observed for Form II crystal of the orthoformate derivative, which exhibited an intramolecular dipolar SO⋯CO (sulfonyl–carbonyl) short contact. An interesting feature in all conformational polymorphs is the formation of an isostructural string (despite the differences in the orientation of the tosyl group) linked via dipolar (ether) O⋯CO contacts, which is further stitched by other weak interactions to form different layers in their crystal lattice.

Two modes of O--H...O hydrogen bonding utilized in dimorphs of racemic 6-O-acryloyl-2-O-benzoyl-myo-inositol 1,3,5-orthoformate.

The title compound, C(17)H(16)O(8), yields conformational dimorphs [forms (I) and (II)] at room temperature, separately or concomitantly, depending on the solvent of crystallization. The yield of crystals of form (I) is always much more than that of crystals of form (II). The molecule has one donor -OH group that can make intermolecular O-H...O hydrogen bonds with one of the two acceptor C=O groups, as well as with the hydroxyl O atom; interestingly, each of the options is utilized separately in the dimorphs. The crystal structure of form (I) contains one molecule in the asymmetric unit and is organized as a planar sheet of centrosymmetric dimers via O-H...O hydrogen bonds involving the OH group and the carbonyl O atom of the acryloyl group. In the crystal structure of form (II), which contains two independent molecules in the asymmetric unit, two different O-H...O hydrogen bonds, viz. hydroxyl-hydroxyl and hydroxyl-carbonyl (benzoyl), connect the molecules in a layered arrangement. Another notable feature is the transformation of form (II) to form (I) via melt crystallization upon heating to 411 K. The higher yield of form (I) during crystallization and the thermal transition of form (II) to form (I) suggest that the association in form (I) is more highly favoured than that in form (II), which is valuable in understanding the priorities of molecular aggregation during nucleation of various polymorphs.

Ionic hydrogenation of C-20, 22-ketene dithioacetal: stereoselective synthesis of steroidal C (20R) aldehydes

Homologation of 16-dehydropregnenolone acetate leads to excellent stereocontrolled synthesis of unnatural C (20R) aldehydes and through compound .