N…N pnicogen bonds in Boc-DOPA-OMe Tripathi, Garima; Badi-uz-zama, Khalid; Ramanathan, Gurunath
Chemical physics letters,
06/2016, Letnik:
653
Journal Article
Recenzirano
Crystal structures of Boc-DOPA-OMe in racemic (rac) and homochiral (S, chi) form were determined. Pnicogen bonds were observed in both forms, bifurcating the 10-membered ring, supported by ...theoretical studies. Display omitted
•Crystal structures of Boc-DOPA-OMe in racemic and homochiral (S) form were determined.•Presence of N…N pnicogen interaction is seen in crystals of both forms and supported by QTAIM calculations.•Determination of stabilization energies of these interactions.
Crystal structures of Boc-DOPA-OMe in racemic and homochiral (S) form were determined and found to be similar in terms of supramolecular organization. The computation of electron density and its topological analysis provided insight into the interactions of the molecules within their crystal environments. The presence of N…N pnicogen bonds in both crystals was also predicted by QTAIM calculations, which are reported for the first time in amino acid systems.
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•The ZWIX(+) column allowed getting the Boc-Aph(Hor)-OH (1) isomeric peaks resolved.•ECD studies and molecular dynamic simulations allowed to assign the elution order.•Molecular ...descriptors revealed the active role of achiral elements of the CSP.
A chiral chromatography method enabling the simultaneous diastereo- and enantioseparation of Nα-Boc-N4-(hydroorotyl)-4-aminophenylalanine Boc-Aph(Hor)-OH, 1 was optimized with a quinine-based zwitterionic stationary phase. The polar-ionic eluent system consisting of ACN:MeOH:water—49.7:49.7:0.6 (v/v/v) with formic acid (4.0mM) and diethylamine (2.5mM), allowed the successful separation of the four acid stereoisomers: αd,d-/d,l-1=1.08; αd,l-/l,d-1=1.08; αl,d-/l,l-1=1.40.
According to the in-house developed synthetic procedure and the recorded electronic circular dichroism spectra, the following stereoisomeric elution order was readily established in the optimal chromatographic conditions: d,d-1<d,l-1<l,d-1<l,l-1.
With the aim of better understanding the molecular basis of the retention behaviour of the four stereoisomers in the employed chromatographic system and conditions, a computational protocol consisting in molecular dynamics simulations was applied. The use of the three descriptors INTER (in kcalmol−1, encoding for the interaction energy between the selector SO unit and the whole system), INTER_SA (in kcalmol−1, encoding for the interaction energy between SO and the sole selectand SA), and SELF (in kcalmol−1, encoding for the conformational energy of SA relative to its minimum energy registered by the collected snapshots) revealed the active role of achiral sub-structural elements of the chiral stationary phase and eluent components in the overall stereorecognition mechanism.
•Synthesis of polymerizable TLAs as the styrene and methacrylate derivatives.•Therman deprotection and decomposition behavior of the TLA homopolymers.•Copolymerization of PBHEMA with the TLAs and the ...characterization of the resulting copolymers.•Achievement of thermal stability during storage and quick deprotection on heating using the methacrylate -type TLAs.
Poly((2‑tert-butoxycarbonyloxy)ethyl methacrylate) (PBHEMA) is converted to poly(2-hydroxyethyl methacrylate) (PHEMA) with the release of isobutene and CO2 by heating and this reaction is accelerated by an acid. The thermally latent acid catalysts (TLA) are useful for the control of a working temperature for the deprotection of the tert‑butoxycarbonyl (BOC) groups included in PBHEMA. In this study, styrene- and methacrylate-type sulfonic esters were synthesized and copolymerized with BHEMA in order to investigate the effect of the TLAs incorporated into the polymer chains. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out for the copolymers of BHEMA with the polymerizable TLAs in order to discuss the deprotection features of the BOC group in comparison with the results for the systems of PBHEMA blended with the low-molecular-weight TLAs.
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t‐Butyl‐oxycarbonylated diamines (“di‐Boc‐carbamates”) are investigated as dicarbamate monomers for diamine/dicarbamate polymerizations. Polyureas (PUs) and polyurethanes (PURs) with high molecular ...weights are prepared from stoichiometric polymerizations of diamines or diols with N‐N′‐di‐t‐butyl‐oxycarbonyl isophorone diamine (DiBoc‐IPDC) using KOt‐Bu as a catalyst, while gelation is observed when an excess of DiBoc‐IPDC is used with respect to the diamines or diols. Stable dispersions are obtained from PUs and PURs with 3,3′‐diamino‐N‐methyldipropylamine (DMDPA) as internal dispersing agent. The corresponding PU‐based coatings exhibit superior mechanical properties and solvent resistances compared to the polyurethane urea coatings synthesized from diols, DiBoc‐IPDC, and DMDPA.
Polyurethane/ureas with high molecular weights are synthesized from DiBoc‐carbamates and diamines. The study on the mechanism of the polymerization indicates the formation of isocyanate intermediates during the Boc‐carbamate/amine reactions in the presence of alkali alkoxides. Stable water‐borne polyurethane/urea dispersions are successfully prepared based on this reaction and the corresponding coatings exhibit satisfactory material properties.
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•The In-doped Bi2O2CO3 nanosheets was prepared by in-situ transformation of In-doped Bi nanoblocks.•A maximum FEformate nearly 100% was achieved at −0.9 V vs. RHE with high ...stability.•An average FEformate of 93.5% was achieved in a wide potential window of 450 mV.•The incorporation of In into Bi2O2CO3 enhanced the adsorption of CO2, CO2*- and *OCOH.
Electrochemical carbon dioxide (CO2) reduction reaction (E-CO2RR) to formate with high selectivity driven by renewable electricity is one of the most promising routes to carbon neutrality. Herein, we developed a novel indium (In)-doped bismuth subcarbonate (BOC) nanosheets (BOC-In-x NSs) through transformation of In-doped bismuth (Bi) nanoblocks (Bi-In-x NBs). The BOC-In-0.1 NSs achieved a maximum Faraday efficiency of formate (FEformate) nearly 100% with high stability (22 h) and an appreciable average FEformate of 93.5% in a wide potential window of 450 mV. The experimental and theoretical calculations indicate that the incorporation of In into BOC nanosheets enhanced the adsorption of CO2 and the intermediates during the process of E-CO2RR, and reduced the energy barrier for the formation of formate.
A facile and versatile method for the chemoselective Boc protection of amines has been developed by a treatment with (Boc)2O in the presence of sulfonic-acid-functionalized silica as a catalyst. The ...method is general for the preparation of N-Boc derivatives of aliphatic (acyclic and cyclic), aromatic, and heteroaromatic amines; primary and secondary amines; aminols, amino-esters; and sulfonamides. The catalyst works under heterogeneous conditions and can be recycled.
The chemoselective N-acylation of non-nucleophilic nitrogen heterocycles including indoles, pyrroles, pyrazole, and imidazole using ethyl 2-(tert-butoxycarbonyloxyimino)-2-cyanoacetate (Boc-Oxyma) ...under ambient conditions, which eludes purification and proceeds relatively fast with excellent yields, is reported. The substrate scope is broad, and the methodology is tolerant towards many other functional groups such as ester, aldehyde, nitro, iodo, bromo, cyano, and others. In addition to the methodology, the effect of base, solvent, temperature, and the mechanistic pathway is studied.
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•Extensively used in medicinal chemistry, as aminoacylating agents in the synthesis of aminoacyl-tRNA analogs.•Used in peptide, dendrimer, buckyball amino acid, protection for ...carboxylic acids chemistry and resolution of amines.•Achieving pure aminoacid cyanomethyl esters with an unprotected amine group remain a challenge.•Here in cyanomethyl esters N-deprotection were isolated and well characterised by adequate analytical data.
A number of cyanomethyl esters of natural/unnatural aminoacids with un-protected amino functionality were synthesized because of their synthetic and medicinal importance. Critical N-Boc deprotection methods in the presence of labile (hydrolytic sensitivity) cyanomethyl functionality were screened thoroughly and it was found that readily available 4M HCl in 1,4-dioxane solution (2–4 equiv); acetonitrile, 0 °C, 2–4 h was a suitable condition. This condition was generalized and successfully applied to a variety of alkyl, alkynyl, aryl, heteroaryl, benzyl, azido, spiro amino acid cyanomethylesters irrespective of the nature of the amine (primary or secondary) and the distance between the amine and ester group to achieve final deprotected amino esters with high yield, and purity compared to other commonly known N-protecting groups (Cbz, Fmoc, Ac, Bn, Bz etc.). It was also demonstrated that N-Boc protected aminoacid cyanomethylesters are stable enough to carry out further functionalization compared to N-unprotected counterparts.
Trong nghiên cứu này, vật liệu graphene (GR) được chế tạo từ thanh graphite sử dụng phương pháp bóc tách điện hóa với các loại điện áp khác nhau đặt vào hai đầu điện cực, bao gồm các điện áp không ...đổi 6 V, 8 V, 10 V và kỹ thuật thế bậc thang hai giai đoạn từ 0-2 V và 2-10 V trong môi trường ammonium sulfate (NH4)2SO4. Kết quả chế tạo đã được khảo sát bằng các phép đo thế Zeta, kính hiển vi điện tử quét phát xạ trường (FE-SEM), kính hiển vi lực nguyên tử (AFM) và quang phổ Raman để xác định đặc trưng và cấu trúc của vật liệu GR. Thế Zeta thu được của GR-010 có giá trị -47,7 mV cho thấy hiệu quả phân tán trong môi trường nước, hiệu quả này do khả năng liên kết tốt với các ion âm ở bề mặt và biên của GR. Kết quả đo SEM và AFM cũng chỉ ra bề dày trung bình của các tấm GR-010 thu được vào cỡ 1,8 nm tương ứng 3-5 lớp GR, nhỏ hơn so với các mẫu GR-6, GR-8 và GR-10 tương ứng với các điện áp 6 V, 8 V và 10 V. Kết quả phân tích Raman cũng cho thấy mức độ sai hỏng của GR-010 thấp hơn so với GR-6, GR-8 và GR-10 với tỷ số ID/IG = 0,36.
