@article {44535, title = {N-Heterocyclic carbene-catalyzed michael-michael-lactonization cascade for the enantioselective synthesis of tricyclic delta-lactones}, journal = {Organic Letters}, volume = {20}, year = {2018}, month = {MAY}, pages = {2952-2955}, abstract = {

Enantioselective synthesis of tricyclic delta-lactones with three contiguous stereocenters has been demonstrated by the N-heterocyclic carbene (NHC)-catalyzed functionalization of benzylic C(sp(3))-H bonds. The NHC-catalyzed reaction of enals with dinitrotoluene derivatives under oxidative conditions proceeds via the chiral alpha,beta-unsaturated acylazoliums and produces the delta-lactones in good yields and excellent diastereoselectivity and enantioselectivity. This mild and atom-economic cascade reaction takes place in a Michael/Michael/lactonization sequence and tolerates a broad range of functional groups.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.8b00998}, author = {Mukherjee, Subrata and Ghosh, Arghya and Marelli, Udaya Kiran and Biju, Akkattu T.} } @article {44597, title = {N-Methylation of isoDGR peptides: discovery of a selective alpha 5 beta 1-integrin ligand as a potent tumor imaging agent}, journal = {Journal of Medicinal Chemistry}, volume = {61}, year = {2018}, month = {MAR}, pages = {2490-2499}, type = {Article}, abstract = {

Specific targeting of the integrin subtype alpha 5 beta 1 possesses high potential in cancer diagnosis and therapy. Through sequential N-methylation, we successfully converted the biselective alpha 5 beta 1/alpha v beta 6 peptide c(phg-isoDGR-k) into a potent peptidic RGD binding aSfil subtype selective ligand c(phg-isoDGR-(NMe)k). Nuclear magnetic resonance spectroscopy and molecular modeling clarified the molecular basis of its improved selectivity profile. To demonstrate its potential in vivo, c(phg-isoDGR-(NMe)k) was trimerized with the chelator TRAP and used as a positron-emission tomography tracer for monitoring alpha 5 beta 1 integrin expression in a M21 mouse xenograft.

}, issn = {0022-2623}, doi = {10.1021/acs.jmedchem.7b01752}, author = {Kapp, Tobias G. and Di Leva, Francesco Saverio and Notni, Johannes and Raeder, Andreas F. B. and Fottner, Maximilian and Reichart, Florian and Reich, Dominik and Wurzer, Alexander and Steiger, Katja and Novellino, Ettore and Marelli, Udaya Kiran and Wester, Hans-Juergen and Marinelli, Luciana and Kessler, Horst} } @article {46021, title = {N-Heterocyclic carbene-catalyzed umpolung of imines for the enantioselective synthesis of dihydroquinoxalines}, journal = {ACS Catalysis}, volume = {9}, year = {2019}, month = {MAY}, pages = {4065-4071}, type = {Article}, abstract = {

N-heterocyclic carbene (NHC) organocatalysis is widely employed for the umpolung of aldehydes and recently to the umpolung of Michael acceptors and aldimines. Described herein is the NHC-organocatalyzed umpolung of aldimines for the enantioselective synthesis of nitrogen heterocycles. The bisimines generated from the condensation of 1,2-phenylenediamines and salicylaldehydes undergo intramolecular cyclization in the presence of a chiral NHC catalyst, resulting in the formation of dihydroquinoxalines in moderate to good yields and er values. Detailed DFT studies shed light on the role of -OH groups in stabilizing the initially generated aza-Breslow intermediates via intramolecular hydrogen bonds. Preliminary photophysical studies on the synthesized dihydroquinoxalines revealed that these molecules can be used for the sensing of various acids and bases.

}, keywords = {dihydroquinoxalines, imines, N-heterocyclic carbenes, organocatalysis, umpolung}, issn = {2155-5435}, doi = {10.1021/acscatal.9b00737}, author = {Das, Tamal Kanti and Ghosh, Avik and Balanna, Kuruva and Behera, Pradipta and Gonnade, Rajesh G. and Marelli, Udaya Kiran and Das, Abhijit Kumar and Biju, Akkattu T.} } @article {46899, title = {N-heterocyclic carbene catalysis exploiting oxidative imine umpolung for the generation of imidoyl azoliums}, journal = {Journal of Organic Chemistry}, volume = {85}, year = {2020}, month = {APR }, pages = {5114-5121}, type = {Article}, abstract = {

Although NHC-catalyzed umpolung of imines are known, the related reactions under oxidative conditions are limited. Described herein is the two-step process involving the initial formation of aldimines from the corresponding aldehydes and 2-amino benzyl alcohols followed by NHC-catalyzed cyclization proceeding via the imidoyl azoliums under oxidative conditions. The reaction allowed the synthesis of trifluoromethylated 3,1-benzoxazines in good yields and broad scope. The role of NHC in the intramolecular cyclization and preliminary mechanistic experiments are also provided.

}, issn = {0022-3263}, doi = {10.1021/acs.joc.0c00360}, author = {Das, Tamal Kanti and Madica, Krishnaprasad and Krishnan, Jagadeesh and Marelli, Udaya Kiran and Biju, Akkattu T.} } @article {46894, title = {Novel cilengitide-based cyclic RGD peptides as alpha nu beta(3) integrin inhibitors}, journal = {Bioorganic \& Medicinal Chemistry Letters}, volume = {30}, year = {2020}, month = {APR}, pages = {127039}, type = {Article}, abstract = {

In this letter, we report a series of five new RGD-containing cyclic peptides as potent inhibitors to alpha nu beta(3) integrin protein. We have incorporated various unnatural lipophilic amino acids into the cyclic RGD framework of cilengitide, which is selective for alpha nu beta(3) integrin. All the newly synthesized cyclic peptides were evaluated in vitro solid phase binding assay and investigated for their binding behaviour towards integrin subtypes. All the cyclic peptides were synthesized in excellent yield following solution-phase coupling strategy. The cyclic RGD peptides 1a-e exhibited IC50 of 9.9, 5.5, 72, 11 and 3.3 nM, respectively, towards a alpha nu beta(3) integrin protein. This finding offers further opportunities for the introduction unusual amino acids into the cyclic peptide framework of cilengitide.

}, keywords = {Anticancer drugs, Cilengitide, Integrins, RGD cyclicpeptides}, issn = {0960-894X}, doi = {10.1016/j.bmcl.2020.127039}, author = {Meena, Chhuttan L. and Singh, Dharmendra and Weinmueller, Michael and Reichart, Florian and Dangi, Abha and Marelli, Udaya Kiran and Zahler, Stefan and Sanjayan, Gangadhar J.} }