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Paramjit S Arora

Publications and source records attributed to Paramjit S Arora.

12 recordsLinked to original sources
PubMed2006

Optimized synthesis of hydrogen-bond surrogate helices: surprising effects of microwave heating on the activity of Grubbs catalysts.

This manuscript discusses microwave-assisted solid-phase synthesis of hydrogen-bond surrogate based alpha-helices and analogues by ring-closing metathesis (RCM). Microwave-mediated RCM allows access to a greater variety of amino acid residues in the macrocycles in shorter reaction times and higher yields compared to conventional heating. Surprisingly, we discovered that the Grubbs II catalyst is highly active under the influence of microwaves but catalytically dead under oil-bath conditions for the metathesis of these peptide bisolefins. [reaction: see text]

Alkenes↗
PubMed2006

Evaluation of biologically relevant short alpha-helices stabilized by a main-chain hydrogen-bond surrogate.

We previously reported the design and synthesis of a new class of artificial alpha-helices in which an N-terminal main-chain hydrogen bond is replaced by a carbon-carbon bond derived from a ring-closing metathesis reaction [Chapman, R. N.; Dimartino, G.; Arora, P. S. J. Am. Chem. Soc. 2004, 126, 12252-12253]. Our initial study utilized an alanine-rich sequence; in the present manuscript we evaluate the potential of this method for the synthesis of very short (10 residues) alpha-helices representing two different biologically relevant alpha-helical domains. We extensively characterized these two sets of artificial helices by NMR and circular dichroism spectroscopies and find that the hydrogen-bond surrogate approach can afford well-defined short alpha-helical structures from sequences that do not spontaneously form alpha-helical conformations.

Amino Acid Sequence↗
PubMed2005

Nonpeptidic foldamers from amino acids: synthesis and characterization of 1,3-substituted triazole oligomers.

Nonpeptidic foldamers capable of displaying protein-like functionality were prepared by swapping amide bonds with 1,2,3-triazole rings. The overall conformation of these triazole oligomers is largely dictated by dipole-dipole interactions between adjacent rings. Solution NMR studies suggest that a zigzag conformation, which closely mimics the beta-strand structure, predominates in two different tetramers.

Amino Acids↗
PubMed2005

Solid-phase synthesis of hydrogen-bond surrogate-derived alpha-helices.

[reaction: see text] This report describes the solid-phase synthesis of hydrogen-bond surrogate-derived artificial alpha-helices by a ring-closing metathesis reaction. From a series of metathesis catalysts evaluated for the synthesis of these helices, the Hoveyda-Grubbs catalyst was found to afford high yields of the macrocycle irrespective of the peptide sequence.

Catalysis↗
PubMed2005

Adding specificity to artificial transcription activators.

In this issue, Mapp and colleagues describe a significant advance in the design of artificial transcription activators that function in a cell-type-specific manner. [1] The authors show that peptides selected for binding a component of the yeast transcription complex require its presence for effective transcriptional activation.

Gene Expression Regulation, Fungal↗
PubMed2004

A highly stable short alpha-helix constrained by a main-chain hydrogen-bond surrogate.

Herein we describe a strategy for the preparation of artificial alpha-helices involving replacement of one of the main-chain hydrogen bonds with a covalent linkage. To mimic the C=O...H-N hydrogen bond as closely as possible, we envisioned a covalent bond of the type C=X-Y-N, where X and Y are two carbon atoms connected through an olefin metathesis reaction. Our results demonstrate that the replacement of a hydrogen bond between the i and i + 4 residues at the N-terminus of a short peptide with a carbon-carbon bond results in a highly stable constrained alpha-helix at physiological conditions as indicated by CD and NMR spectroscopies. The advantage of this strategy is that it allows access to short alpha-helices with strict preservation of molecular recognition surfaces required for biomolecular interactions.

Alanine↗
PubMed2004

Arresting cancer proliferation by small-molecule gene regulation.

A small library of pyrrole-imidazole polyamide-DNA alkylator (chlorambucil) conjugates was screened for effects on morphology and growth characteristics of a human colon carcinoma cell line, and a compound was identified that causes cells to arrest in the G2/M stage of the cell cycle. Microarray analysis indicates that the histone H4c gene is significantly downregulated by this polyamide. RT-PCR and Western blotting experiments confirm this result, and siRNA to H4c mRNA yields the same cellular response. Strikingly, reduction of H4 protein by >50% does not lead to widespread changes in global gene expression. Sequence-specific alkylation within the coding region of the H4c gene in cell culture was confirmed by LM-PCR. The compound is active in a wide range of cancer cell lines, and treated cells do not form tumors in nude mice. The compound is also active in vivo, blocking tumor growth in mice, without obvious animal toxicity.

Antineoplastic Agents, Alkylating↗
PubMed2003

A ribozyme with michaelase activity: synthesis of the substrate precursors.

The ability to generate RNA molecules that can catalyze complex organic transformations not only facilitates the reconstruction and plausibility of possible prebiotic reaction pathways but is also crucial for elucidating the potential of the application of RNA catalysts in organic syntheses. Iterative RNA selection previously identified a ribozyme that catalyzes the Michael addition of a cysteine thiol to an alpha,beta-unsaturated amide. This reaction is chemically similar to the rate limiting step of the thymidylate synthase reaction, which is the corresponding reaction of a cysteine thiol to the double-bond of the uracil nucleobase. Here we provide a detailed description of the synthesis of the ribozyme substrates and the substrate oligonucleotides used for its characterization and the investigation of the background reaction. We also describe the further characterization of the ribozyme with respect to substrate specificity. We show that the thiol group of the cysteine nucleophile is essential for the reaction to proceed. When substituted for a thiomethyl group, no reaction takes place.

Amides↗
PubMed2002

Design of artificial transcriptional activators with rigid poly-L-proline linkers.

Typical eukaryotic transcriptional activators are composed of distinct functional domains, including a DNA binding domain and an activating domain. Artificial transcription factors have been designed wherein the DNA binding domain is a minor groove DNA binding hairpin polyamide linked by a flexible tether to short activating peptides, typically 16-20 residues in size. In this study, the linker between the polyamide and the peptide was altered in an incremental fashion using rigid oligoproline "molecular rulers" in the 18-45 A length range. We find that there is an optimal linker length which separates the DNA and the activation region for transcription activation.

Amino Acid Sequence↗
PubMed2002

Cellular uptake of N-methylpyrrole/N-methylimidazole polyamide-dye conjugates.

The cellular uptake and localization properties of DNA binding N-methylpyrrole/N-methylimidazole polyamide-dye conjugates in a variety of living cells have been examined by confocal laser scanning microscopy. With the exception of certain T-cell lines, polyamide-dye conjugates localize mainly in the cytoplasm and not in the nucleus. Reagents such as methanol typically used to fix cells for microscopy significantly alter the cellular localization of these DNA-binding ligands.

Boron Compounds↗