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1. Mimicking Microbial Rhodopsin Isomerization in a Single Crystal

Author:
Borhan, Babak,   et al.   ; Ghanbarpour, Alireza; Nairat, Muath; Nosrati, Meisam; Santos, Elizabeth M.; Vasileiou, Chrysoula; Dantus, Marcos; Geiger, James H.;     Show all 8 Authors
Source:
Journal of the American Chemical Society 2018 v.141 no.4 pp. 1735-1741
ISSN:
1520-5126
Subject:
isomers; mutation; photoisomerization; photons; rhodopsin; transmembrane proteins
Abstract:
... Bacteriorhodopsin represents the simplest, and possibly most abundant, phototropic system requiring only a retinal-bound transmembrane protein to convert photons of light to an energy-generating proton gradient. The creation and interrogation of a microbial rhodopsin mimic, based on an orthogonal protein system, would illuminate the design elements required to generate new photoactive proteins wit ...
DOI:
10.1021/jacs.8b12493

2. Cu-Catalyzed Oxidation of C2 and C3 Alkyl-Substituted Indole via Acyl Nitroso Reagents

Author:
Borhan, Babak,   et al.   ; Zhang, Jun; Torabi Kohlbouni, Saeedeh;     Show all 3 Authors
Source:
Organic letters 2018 v.21 no.1 pp. 14-17
ISSN:
1523-7052
Subject:
amination; chemical structure; indoles; oxidation
Abstract:
... The selective oxidation of C2-alkyl-substituted indoles to 3-oxindole and the selective C–H oxygenation or amination of C2,C3-dialkyl-substituted indoles at C2 are reported under mild conditions. The position of the alkyl substitution on the indole directs the reaction to different pathways under similar conditions. ...
DOI:
10.1021/acs.orglett.8b03185

3. Free-Energy-Based Protein Design: Re-Engineering Cellular Retinoic Acid Binding Protein II Assisted by the Moveable-Type Approach

Author:
Borhan, Babak,   et al.   ; Zhong, Haizhen A.; Santos, Elizabeth M.; Vasileiou, Chrysoula; Zheng, Zheng; Geiger, James H.; Merz, Kenneth M.;     Show all 7 Authors
Source:
Journal of the American Chemical Society 2018 v.140 no.10 pp. 3483-3486
ISSN:
1520-5126
Subject:
Gibbs free energy; amino acids; binding capacity; binding proteins; binding sites; models; molecular dynamics; mutagenesis; mutants; protein engineering; retinoic acid
Abstract:
... How to fine-tune the binding free energy of a small-molecule to a receptor site by altering the amino acid residue composition is a key question in protein engineering. Indeed, the ultimate solution to this problem, to chemical accuracy (±1 kcal/mol), will result in profound and wide-ranging applications in protein design. Numerous tools have been developed to address this question using knowledge ...
DOI:
10.1021/jacs.7b10368

4. Absolute Stereochemical Determination of Asymmetric Sulfoxides via Central to Axial Induction of Chirality

Author:
Borhan, Babak,   et al.   ; Gholami, Hadi; Zhang, Jun; Anyika, Mercy;     Show all 4 Authors
Source:
Organic letters 2017 v.19 no.7 pp. 1722-1725
ISSN:
1523-7052
Subject:
chemical structure; optical isomerism; organic compounds; stereochemistry
Abstract:
... The absolute configuration of chiral sulfoxides is determined by means of host–guest complexation that leads to the induction of axial chirality in an achiral host. The central to axial induction of helicity is rationalized by a simple recognition of the relative length and size of the substituents attached to the S-center. This technique is used to determine the absolute configuration of chiral s ...
DOI:
10.1021/acs.orglett.7b00495

5. Computationally Aided Absolute Stereochemical Determination of Enantioenriched Amines

Author:
Borhan, Babak,   et al.   ; Zhang, Jun; Gholami, Hadi; Ding, Xinliang; Chun, Minji; Vasileiou, Chrysoula; Nehira, Tatsuo;     Show all 7 Authors
Source:
Organic letters 2017 v.19 no.6 pp. 1362-1365
ISSN:
1523-7052
Subject:
chemical reactions; circular dichroism spectroscopy; molecular conformation; monoamines; stereochemistry
Abstract:
... A simple and efficient protocol for sensing the absolute stereochemistry and enantiomeric excess of chiral monoamines is reported. Preparation of the sample requires a single-step reaction of the 1,1′-(bromomethylene)dinaphthalene (BDN) with the chiral amine. Analysis of the exciton coupled circular dichroism generated from the BDN-derivatized chiral amine sample, along with comparison to conforma ...
DOI:
10.1021/acs.orglett.7b00246

6. Highly Regio- and Enantioselective Vicinal Dihalogenation of Allyl Amides

Author:
Borhan, Babak,   et al.   ; Soltanzadeh, Bardia; Jaganathan, Arvind; Yi, Yi; Yi, Hajoon; Staples, Richard J.;     Show all 6 Authors
Source:
Journal of the American Chemical Society 2017 v.139 no.6 pp. 2132-2135
ISSN:
1520-5126
Subject:
amides; catalysts; enantiomers; salts
Abstract:
... We report a highly regio-, diastereo- and enantioselective vicinal dihalogenation of allyl amides. E- and Z-alkenes with both aryl and alkyl substituents were compatible with this chemistry. This is the result of exquisite catalyst controlled regioselectivity enabling use of electronically unbiased substrates. The reaction employs commercially available catalysts and halenium sources along with ch ...
DOI:
10.1021/jacs.6b09203

7. Mechanistically Inspired Route toward Hexahydro-2H-chromenes via Consecutive [4 + 2] Cycloadditions

Author:
Borhan, Babak,   et al.   ; Ashtekar, Kumar Dilip; Ding, Xinliang; Toma, Edmond; Sheng, Wei; Gholami, Hadi; Rahn, Christopher; Reed, Paul;     Show all 8 Authors
Source:
Organic letters 2016 v.18 no.16 pp. 3976-3979
ISSN:
1523-7052
Subject:
chemical bonding; chemical structure; cycloaddition reactions; diastereoselective synthesis; organic compounds; stereoselectivity
Abstract:
... Utilizing two robust C–C bond-forming reactions, the Baylis–Hillman reaction and the Diels–Alder reaction, we report a highly enantio-, regio-, and diastereoselective synthesis of hexahydro-2H-chromenes via two sequential [4 + 2] cycloadditions. These tandem and formal cycloadditions have also been performed as a “one-pot” sequence to access the corresponding heterocycles constituting up to five c ...
DOI:
10.1021/acs.orglett.6b01742
PubMed:
27487461
PubMed Central:
PMC5342895

8. A Photoisomerizing Rhodopsin Mimic Observed at Atomic Resolution

Author:
Borhan, Babak,   et al.   ; Nosrati, Meisam; Berbasova, Tetyana; Vasileiou, Chrysoula; Geiger, James H.;     Show all 5 Authors
Source:
Journal of the American Chemical Society 2016 v.138 no.28 pp. 8802-8808
ISSN:
1520-5126
Subject:
binding proteins; isomerization; isomers; lipids; rhodopsin; schiff bases
Abstract:
... The members of the rhodopsin family of proteins are involved in many essential light-dependent processes in biology. Specific photoisomerization of the protein-bound retinylidene PSB at a specified wavelength range of light is at the heart of all of these systems. Nonetheless, it has been difficult to reproduce in an engineered system. We have developed rhodopsin mimics, using intracellular lipid ...
DOI:
10.1021/jacs.6b03681

9. Nucleophile-Assisted Alkene Activation: Olefins Alone Are Often Incompetent

Author:
Borhan, Babak,   et al.   ; Ashtekar, Kumar Dilip; Vetticatt, Mathew; Yousefi, Roozbeh; Jackson, James E.;     Show all 5 Authors
Source:
Journal of the American Chemical Society 2016 v.138 no.26 pp. 8114-8119
ISSN:
1520-5126
Subject:
alkenes; chemical interactions; enantiomers; isotopes; spectroscopy; stereoisomerism
Abstract:
... Emerging work on organocatalytic enantioselective halocyclizations naturally draws on conditions where both new bonds must be formed under delicate control, the reaction regime where the concerted nature of the AdE3 mechanism is of greatest importance. Without assistance, many simple alkene substrates react slowly or not at all with conventional halenium donors under synthetically relevant reactio ...
DOI:
10.1021/jacs.6b02877
PubMed:
27284808
PubMed Central:
PMC5340197

10. “Turn-On” Protein Fluorescence: In Situ Formation of Cyanine Dyes

Author:
Borhan, Babak,   et al.   ; Yapici, Ipek; Lee, Kin Sing Stephen; Berbasova, Tetyana; Nosrati, Meisam; Jia, Xiaofei; Vasileiou, Chrysoula; Wang, Wenjing; Santos, Elizabeth M.; Geiger, James H.;     Show all 10 Authors
Source:
Journal of the American Chemical Society 2015 v.137 no.3 pp. 1073-1080
ISSN:
1520-5126
Subject:
binding proteins; dyes; fluorescence; fluorescent proteins; mutants; mutation; pH; retinoic acid; spectroscopy
Abstract:
... Protein reengineering of cellular retinoic acid binding protein II (CRABPII) has yielded a genetically addressable system, capable of binding a profluorophoric chromophore that results in fluorescent protein/chromophore complexes. These complexes exhibit far-red emission, with high quantum efficiencies and brightness and also exhibit excellent pH stability spanning the range of 2–11. In the course ...
DOI:
10.1021/ja506376j
PubMed:
25534273
PubMed Central:
PMC4311949

11. A New Tool To Guide Halofunctionalization Reactions: The Halenium Affinity (HalA) Scale

Author:
Borhan, Babak,   et al.   ; Ashtekar, Kumar Dilip; Marzijarani, Nastaran Salehi; Jaganathan, Arvind; Holmes, Daniel; Jackson, James E.;     Show all 6 Authors
Source:
Journal of the American Chemical Society 2014 v.136 no.38 pp. 13355-13362
ISSN:
1520-5126
Subject:
alkenes; amides; amines; chemical reactions; ions; oxygen; prediction
Abstract:
... We introduce a previously unexplored parameterhalenium affinity (HalA)– as a quantitative descriptor of the bond strengths of various functional groups to halenium ions. The HalA scale ranks potential halenium ion acceptors based on their ability to stabilize a “free halenium ion”. Alkenes in particular but other Lewis bases as well, such as amines, amides, carbonyls, and ether oxygen atoms, etc. ...
DOI:
10.1021/ja506889c

12. Chlorosulfonamide Salts Are Superior Electrophilic Chlorine Precursors for the Organocatalytic Asymmetric Chlorocyclization of Unsaturated Amides

Author:
Borhan, Babak,   et al.   ; Jaganathan, Arvind;     Show all 2 Author
Source:
Organic letters 2014 v.16 no.14 pp. 3616-3619
ISSN:
1523-7052
Subject:
Lewis acids; alkenes; ambient temperature; amides; catalytic activity; chemical reactions; chemical structure; chlorine; salts; stereoselectivity
Abstract:
... Chloramine-T·3H₂O and other chlorosulfonamide salts can serve as readily available, stable, and inexpensive precursors of electrophilic chlorine in the organocatalytic asymmetric chlorofunctionalization of olefins. In conjunction with commercially available organocatalysts, they can be utilized in the asymmetric chlorocyclization of unsaturated amides to yield products with unprecedented levels of ...
DOI:
10.1021/ol500861z

13. Point-to-Axial Chirality TransferA New Probe for “Sensing” the Absolute Configurations of Monoamines

Author:
Borhan, Babak,   et al.   ; Anyika, Mercy; Gholami, Hadi; Ashtekar, Kumar D.; Acho, Robert;     Show all 5 Authors
Source:
Journal of the American Chemical Society 2014 v.136 no.2 pp. 550-553
ISSN:
1520-5126
Subject:
hydrogen bonding; models; monoamines; prediction; stereoisomerism
Abstract:
... A host molecule, capable of freely adopting P or M helicity, is described for molecular recognition and chirality sensing. The host, consisting of a biphenol core, binds chiral amines via hydrogen-bonding interactions. The diastereomeric complex will favor either P or M helicity as a result of minimizing steric interactions of the guest molecule with the binding cavity of the host, resulting in a ...
DOI:
10.1021/ja408317b

14. 7-β- and 10-β-Hydroxylated congeners of CAF-603; elucidation of absolute configuration of CAF-603 family, and their SAR studies in the anti-fungal activity

Author:
Borhan, Babak,   et al.   ; Yasumura, Ryoko; Dilip Ashtekar, Kumar; Tonouchi, Akio; Nehira, Tatsuo; Hashimoto, Masaru;     Show all 6 Authors
Source:
Tetrahedron 2013 v.69 pp. 9469-9474
ISSN:
0040-4020
Subject:
Trichoderma crassum; chemical reactions; chemical structure; cotton; esters; stereochemistry
Abstract:
... Novel 7-β- and 10-β-hydroxylated congeners of CAF-603 (4 and 5, respectively) were isolated from Trichoderma crassum. Relative configuration of 4 was determined by NOE experiments. Stereochemistry of 7-β-hydroxy group in 5 was established by a combination of vicinal 3JH–H analyses and quantum chemical calculations. Absolute configurations of 4 and 5 were established by observing the Cotton effects ...
DOI:
10.1016/j.tet.2013.08.065

15. Rational Design of a Colorimetric pH Sensor from a Soluble Retinoic Acid Chaperone

Author:
Borhan, Babak,   et al.   ; Berbasova, Tetyana; Nosrati, Meisam; Vasileiou, Chrysoula; Wang, Wenjing; Lee, Kin Sing Stephen; Yapici, Ipek; Geiger, James H.;     Show all 8 Authors
Source:
Journal of the American Chemical Society 2013 v.135 no.43 pp. 16111-16119
ISSN:
1520-5126
Subject:
absorption; binding proteins; color; colorimetry; pH; retinoic acid; schiff bases
Abstract:
... Reengineering of cellular retinoic acid binding protein II (CRABPII) to be capable of binding retinal as a protonated Schiff base is described. Through rational alterations of the binding pocket, electrostatic perturbations of the embedded retinylidene chromophore that favor delocalization of the iminium charge lead to exquisite control in the regulation of chromophoric absorption properties, span ...
DOI:
10.1021/ja404900k

16. Dissecting the Stereocontrol Elements of a Catalytic Asymmetric Chlorolactonization: Syn Addition Obviates Bridging Chloronium

Author:
Borhan, Babak,   et al.   ; Yousefi, Roozbeh; Ashtekar, Kumar Dilip; Whitehead, Daniel C.; Jackson, James E.;     Show all 5 Authors
Source:
Journal of the American Chemical Society 2013 v.135 no.39 pp. 14524-14527
ISSN:
1520-5126
Subject:
enantiomers; isotope labeling; nuclear magnetic resonance spectroscopy; olefin; stereochemistry
Abstract:
... We report absolute and relative stereochemistry of addition in enantioselective chlorolactonizations of 4-phenyl-4-pentenoic acid and its related t-butyl ester, catalyzed by (DHQD)₂PHAL. Predominant syn addition of the chlorenium and the nucleophile across the olefin is observed. As shown by isotopic labeling, NMR spectroscopy, and derivative studies, the two new stereocenters formed by addition a ...
DOI:
10.1021/ja4072145

17. Kinetic Resolution of Unsaturated Amides in a Chlorocyclization Reaction: Concomitant Enantiomer Differentiation and Face Selective Alkene Chlorination by a Single Catalyst

Author:
Borhan, Babak,   et al.   ; Jaganathan, Arvind; Staples, Richard J.;     Show all 3 Authors
Source:
Journal of the American Chemical Society 2013 v.135 no.39 pp. 14806-14813
ISSN:
1520-5126
Subject:
amides; catalysts; chlorination; chlorine; enantiomers; hydrogen bonding; olefin; solvents; stereoisomerism
Abstract:
... The first example of a kinetic resolution via chlorofunctionalization of olefins is reported. The enantiomers of racemic unsaturated amides were found to have different hydrogen-bonding affinities for chiral Lewis bases in numerous solvents. This interaction was exploited in developing a kinetic resolution of racemic unsaturated amides via halocyclization. The same catalyst serves to both “sense c ...
DOI:
10.1021/ja407241d

18. Toward an Understanding of the Retinal Chromophore in Rhodopsin Mimics B

Author:
Borhan, Babak,   et al.   ; Huntress, Mark M.; Gozem, Samer; Malley, Konstantin R.; Jailaubekov, Askat E.; Vasileiou, Chrysoula; Vengris, Mikas; Geiger, James H.; Schapiro, Igor; Larsen, Delmar S.; Olivucci, Massimo;     Show all 11 Authors
Source:
The Journal of physical chemistry 2013 v.117 no.35 pp. 10053-10070
ISSN:
1520-5207
Subject:
absorption; actuators; binding proteins; fluorescence; fluorescence emission spectroscopy; isomerization; models; mutants; quantum mechanics; retinoic acid; rhodopsin
Abstract:
... Recently, a rhodopsin protein mimic was constructed by combining mutants of the cellular retinoic acid binding protein II (CRABPII) with an all-trans retinal chromophore. Here, we present a combined computational quantum mechanics/molecular mechanics (QM/MM) and experimental ultrafast kinetic study of CRABPII. We employ the QM/MM models to study the absorption (λᵃₘₐₓ), fluorescence (λᶠₘₐₓ), and re ...
DOI:
10.1021/jp305935t

19. Tuning the Electronic Absorption of Protein-Embedded All-trans-Retinal

Author:
Borhan, Babak,   et al.   ; Wang, Wenjing; Nossoni, Zahra; Berbasova, Tetyana; Watson, Camille T.; Yapici, Ipek; Lee, Kin Sing Stephen; Vasileiou, Chrysoula; Geiger, James H.;     Show all 9 Authors
Source:
Science 2012 v.338 no.6112 pp. 1340-1343
ISSN:
0036-8075
Subject:
absorbance; absorption; animals; microorganisms; mutagenesis; phototaxis; protein binding; retinol-binding protein; rhodopsin; schiff bases; visual perception; wavelengths
Abstract:
... Seeing the Light Rhodopsins respond to a range of electromagnetic radiation—allowing visual perception over a broad wavelength range in animals and facilitating light-driven ion transport and phototaxis in microorganisms. All rhodopsins contain an embedded retinal chromophore in which absorbance is tuned by the protein environment. To gain insight into how the protein tunes absorbance, Wang et al. ...
DOI:
10.1126/science.1226135
PubMed:
23224553
PubMed Central:
PMC4046837

20. 3,4-Dihydroxypyrrolidines via Modified Tandem Aza-Payne/Hydroamination Pathway

Author:
Borhan, Babak,   et al.   ; Kulshrestha, Aman; Salehi Marzijarani, Nastaran; Dilip Ashtekar, Kumar; Staples, Richard;     Show all 5 Authors
Source:
Organic letters 2012 v.14 no.14 pp. 3592-3595
ISSN:
1523-7052
Subject:
Lewis acids; Lewis bases; carbonates; chemical reactions; chemical structure; ethyleneimine
Abstract:
... The outcome of a tandem aza-Payne/hydroamination reaction is modified via the use of a latent nucleophile. The latter initially serves as an electrophile to intercept the aziridine alkoxide and afterward turns into a nucleophile thereby performing the aziridine ring opening, out competing the intramolecular aza-Payne pathway. Subsequent hydroamination in the same pot provides N-Ts enamide carbonat ...
DOI:
10.1021/ol301204w

21. Absolute Configuration for 1,n-Glycols: A Nonempirical Approach to Long-Range Stereochemical Determination

Author:
Borhan, Babak,   et al.   ; Li, Xiaoyong; Burrell, Carmin E.; Staples, Richard J.;     Show all 4 Authors
Source:
Journal of the American Chemical Society 2012 v.134 no.22 pp. 9026-9029
ISSN:
1520-5126
Subject:
circular dichroism spectroscopy; derivatization; porphyrins
Abstract:
... The absolute configurations of 1,n-glycols (n = 2–12, 16) bearing two chiral centers were rapidly determined via exciton-coupled circular dichroism (ECCD) using a tris(pentafluorophenyl)porphyrin (TPFP porphyrin) tweezer system in a nonempirical fashion devoid of chemical derivatization. A unique “side-on” approach of the porphyrin tweezer relative to the diol guest molecule is suggested as the mo ...
DOI:
10.1021/ja2119767

22. A peptide bromoiodinane approach for asymmetric bromolactonization

Author:
Borhan, Babak,   et al.   ; Whitehead, Daniel C.; Fhaner, Matthew;     Show all 3 Authors
Source:
Tetrahedron letters 2011 v.52 no.18 pp. 2288-2291
ISSN:
0040-4039
Subject:
active sites; chemical reactions; enantiomers; organic compounds; peptides
Abstract:
... A series of 37 peptides containing an iodo-aryl amide active site were generated by means of both solid phase and conventional synthesis. These peptides were screened for asymmetric induction in the bromolactonization of 4-phenyl-4-pentenoic acid based on the generation of chiral bromoiodinane bromenium sources. The study culminated in the discovery of a tri-peptide iodo-aryl amide that effected t ...
DOI:
10.1016/j.tetlet.2011.02.056