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Biomedical subjects

Sambasivarao Kotha

Publications and source records attributed to Sambasivarao Kotha.

16 recordsLinked to original sources
PubMed2006

Diversity-oriented approach to biologically relevant molecular frameworks starting with beta-naphthol and using the Claisen rearrangement and olefin metathesis as key steps.

A diversity-oriented approach for the synthesis of various structurally different molecular frameworks from readily accessible and common precursors is described. A Claisen rearrangement followed by ring-closing metathesis or ethylene-promoted ring-closing enyne metathesis has been utilized as the key synthetic transformation to generate naphthoxepine derivatives. The ring-closing metathesis approach has also been used to generate spirocyclic compounds and the pleiadene framework.

Alkenes↗
PubMed2005

Post-assembly peptide modifications by chemical methods.

The demand for peptide drugs is increasing and in this context, "post-assembly (or post-translational) peptide modification strategies" by chemical manipulation of intact oligo-peptides has provided several analogues. Compounds prepared by this method are useful therapeutic molecules for structure activity studies. Herein, we describe various chemical methods such as cross-coupling reactions, cycloaddition reactions, radical reactions and ring-closing metathesis reactions that are useful for post-translational peptide modifications.

Molecular Structure↗
PubMed2004

Conformational switching caused by biphenyl substitution at the Calpha position: ethyl 2-benzyl-2-(formylamino)-3-phenylpropionate and ethyl 3-(1,1'-biphenyl-4-yl)-2-(formylamino)-2-(4-phenylbenzyl)propionate.

The title compounds, C19H21NO3 and C31H29NO3, are derivatives of alpha-aminoisobutyric acid, with benzyl and dibenzyl substitution. The pseudo-peptide formed by the N-formyl and ethyl ester substitution at the Calpha position switches from a trans-trans to a trans-cis configuration as a result of biphenyl substitution. The packing of the compounds is stabilized by N-H...O and C-H...O hydrogen bonds.

Aminoisobutyric Acids↗
PubMed2003

Precursors to dodecahedrane.

The title compounds, (2R,2"S,3b'S,4a'R,7b'S,8a'R)-perhydrodispiro[furan-2,3'-dicyclopenta[a,e]pentalene-7',2"-furan]-5,5"-dione, C(20)H(26)O(4), and (3aR,3bR,4aR,4bS,5aS,8aR,8bR,9aR,9bS,10aS)-perhydrodipentaleno[2,1-a:2',1'-e]pentalene-1,6-dione, C(20)H(26)O(2), are intermediates identified during the synthesis of dodecahedrane. Crystallographic studies have established the ring-junction stereochemistry for these important intermediates. All the ring junctions are cis-fused, and the molecular packing is stabilized by van der Waals interactions.

Journal Article↗
PubMed2003

Ethyl 2-formamido-2-(4-iodobenzyl)-3-(4-iodophenyl)propionate and ethyl 2-(3-bromobenzyl)-3-(3-bromophenyl)-2-formamidopropionate.

The title compounds, C(19)H(19)I(2)NO(3) and C(19)H(19)Br(2)NO(3), are derivatives of alpha-aminoisobutyric acid with halogen substituents at the para and meta positions, respectively. The ethoxycarbonyl and formamide side chains attached to the C(alpha) atom of the molecule adopt extended and folded conformations, respectively. The crystal structures are stabilized by N-H.O, C-H.O, C-Br.O and C-I.O interactions.

Journal Article↗
PubMed2003

Application of the Suzuki-Miyaura cross-coupling reaction for the modification of phenylalanine peptides.

We have demonstrated an exceptionally simple and a useful methodology for modification of unusual phenylalanine peptides by adapting the building block approach using the Suzuki-Miyaura cross-coupling reaction as a key step. This strategy gave a good overall yield of various modified tri- and pentapeptides that may be useful to prepare various biologically active peptides in a short period of time.

Combinatorial Chemistry Techniques↗
PubMed2003

The building block approach to unusual alpha-amino acid derivatives and peptides.

The building block approach was identified as a useful alternative to the commonly used Bücherer-Berg method for the preparation of cyclic unusual alpha-amino acid derivatives. The symmetrical building blocks were prepared by dialkylation of ethyl isocyanoacetate under solid-liquid phase transfer catalysis conditions while the unsymmetrical building blocks were prepared by a stepwise alkylation of the O'Donnell Schiff base. Metathesis reactions, Suzuki couplings, and cycloaddition reactions were utilized to assemble the building blocks.

Amino Acids↗
PubMed2002

Ethyl 6-acetylamino-6,7-dihydro-5H-dibenzo[a,c]cycloheptene-6-carboxylate.

The title compound, C(20)H(21)NO(3), is a derivative of Aib (alpha-aminoisobutyric acid) and is cyclized at the C(alpha) position by biphenyl rings. The seven-membered ring possesses C2 symmetry. The C(alpha) cyclization causes the backbone to assume a helical conformation in the crystal structure. The packing of the molecules is stabilized by intermolecular C-H.O, C-H.pi and N-H.O hydrogen bonds.

Crystallography, X-Ray↗
PubMed2002

First and unexpected synthesis of macrocyclic cyclophane-based unusual alpha-amino acid derivatives by phosphazene base without high dilution conditions.

First synthesis of a macrocylic cyclophane-based unusual alpha-amino acid derivative 11 by coupling of ethyl isocyanoacetate with 1,2-bis(4-bromomethylphenyl)ethane under phase-transfer catalysis (PTC) conditions. Phosphazene base such as 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP) is useful to improve the yield of cyclophane derivative without high dilution conditions.

Amino Acids↗
PubMed2002

Synthesis of constrained phenylalanine derivatives via a [2+2+2] cycloaddition strategy.

A simple synthesis of dialkyne building blocks (6, 7, 8 and 9) embodying amino acid moiety is described. The dialkyne 6 participated in a [2+2+2] cycloaddition reaction with various monoalkynes in presence of Wilkinson's catalyst to give 5- and 5,6-disubstituted indan-based -amino acid derivatives. Cobalt catalyst [e.g., CpCo(CO)2] has also been employed in the synthesis of various 2-indanyl glycine derivatives via co-trimerization reaction of the diyne building blocks 6 and 7 with several monoalkynes.

Cobalt↗