Selective Fmoc and Cbz protection of aromatic amino group in the presence of similar aliphatic function in liquid CO2

The selective protection of an aromatic amino group in the presence of aliphatic amino group in diamines by the action of FmocCl or CbzCl using liquid CO₂ as the solvent has been proposed. The developed method is preparative, does not require complex purification of the product, and meets the principles of green chemistry.     

Fmoc-OPhth,the reagent of Fmoc protection

Fmoc-OSu has been widely used for Fmoc protection of amino groups, especially amino acids, in solid phase peptide synthesis. However, it has been recognized that Fmoc-βAla-OH is formed as a by-product via the Lossen rearrangement during the reaction. Since we reconfirmed the formation of Fmoc-βAla-OH during the preparation of Fmoc-AA-OH by Fmoc-OSu, Fmoc-OPhth was designed and synthesized as a new Fmoc reagent to avoid the formation of Fmoc-βAla-OH. Furthermore, Fmoc protection by Fmoc-OPhth and Fmoc-SPPS were evaluated. The various Fmoc-amino acids prepared by Fmoc-OPhth were carried out in good yields and these are applicable in Fmoc-SPPS.     

Orthogonality and compatibility between Tsc and Fmoc amino-protecting groups

New deprotection conditions that provide a complete orthogonality between Tsc and Fmoc amino-protecting groups are described. The potential of these orthogonal deprotection conditions was then demonstrated by the efficient solid-phase synthesis of branched peptides 20 and 21 using doubly protected amino acids such as Tsc-Lys(Fmoc)-OH 4c and Fmoc-Lys(Tsc)-OH 4d.     

Solid-phase synthesis of oligourea peptidomimetics employing the Fmoc protection strategy.

A solid-phase-Fmoc-based-synthesis strategy is described for oligourea peptidomimetics as well as a convenient general synthesis approach for the preparation of the required building blocks 5a-j and 5k. These are suitable for use in peptide or robot synthesizers, which is illustrated by the synthesis of oligourea peptidomimetics of part of Leu-enkephalin (10) and a neurotensin derivative (17).     

Photochemical ring opening of thymidine and thymine in the presence of primary amines

Irradiation of thymidine or thymine in the presence of tert- butylamine at 0 °C provided ping-opened photoadduct $\text{3}$ which on heating at 70 °C gave 1-tert-butylthymine ($\text{2}$) quantitatively. Synthetic application of this photoexchange reaction with amines has been described.     

Molecular iodine-catalyzed efficient N-Cbz protection of amines

An efficient and selective protection of various structurally and electronically divergent aryl and aliphatic amines with Cbz-Cl in the presence of a catalytic amount of molecular iodine (2 mol%) in methanol with high yields at ambient temperature is presented.     

Synthesis of new imines and amines containing organosilicon groups

The Peterson olefination reaction of terephthalaldehyde with tris(trimethylsilyl)methyl lithium, (Me₃Si)₃CLi, in THF at 0 °C gives 4-[2,2-bis(trimethylsilyl)ethenyl]benzaldehyde (1) and 4,4-bis[2,2-bis(trimethylsilyl)ethenyl]benzene (2). The new aldehyde (1) reacts with variety of amines in ethanol to afford the corresponding imines (3) containing vinylbis(trimethylsilyl) group. The newly synthesized imines (3) can be completely converted into amines containing vinylbis(trimethylsilyl) group with an excess amount of NaBH₄. In the case of N-[4-(2,2-bis(trimethylsilyl)ethenyl)benzyl]-2,6-dimethylaniline LiAlH₄ was used as a reducing agent in THF.     

Photochemical substitution of olefins and aromatic compounds with difluoromethyl radicals bearing ester and phosphonate groups

Efficient and selective substitution of cyclic and acyclic vinyl ethers with photo-generated difluoromethyl radicals bearing ester and phosphonate groups, in the presence of 2,4,6-trimethylpyridine and diphenyl diselenide was successfully carried out to provide the corresponding regioselective unsaturated difluoromethylene adducts selectively. The reaction involves phenylselenyl transfer at an early stage followed by elimination of phenylselenol from the adducts once formed to provide the unsaturated difluoromethylene adducts selectively. This novel photochemical method was successfully extended to aromatic and heteroaromatic substitutions to provide the corresponding α-aryl-α,α-difluoroacetates and α-aryl-α,α-difluoromethylphosphonates in good to moderate yields.     

Synthesis of methacrylate polymer bearing cyanate groups and its chemoselective reaction with amines

A novel reactive polymer containing cyanate groups in the side chain was prepared by free radical polymerization of a cyanate‐containing monomer, 2‐(4‐cyanatophenyl)ethyl methacrylate ( 1 ). The monomer 1 and its polymer, poly[2‐(4‐cyanatophenyl)ethyl methacrylate] (PCPMA), were stable under the air for a long period. The copolymerization of 1 and methyl methacrylate provided the corresponding copolymers with various cyanate contents. The availability of the cyanate‐containing polymers as a reactive polymer was investigated. Model reaction using 4‐cyanatotoluene revealed that a cyanate group reacted with aliphatic amines, whereas no reaction occurred in the presence of water, alcohols, and aromatic amines under mild conditions. Post‐functionalization of PCPMA was demonstrated using aliphatic amines or diamines. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 699–706     

Development of tyrosinase labile protecting groups for amines

[reaction: see text] The development of two novel protecting groups for amines is described. Thus, a range of amines have been converted to ureas, and the deprotection of these upon exposure to mushroom tyrosinase (E.C. 1.14.18.1) has been demonstrated.     

Gelation capability of cysteine-modified cyclo(L-Lys-L-Lys)s dominated by Fmoc and Trt protecting groups

A series of symmetrical peptidomimetics(3–8) based on cysteine-modified cyclo(L-Lys-L-Lys)s were synthesized, and their gelation capability in organic solvents was dominated by fluorenylmethyloxycarbonyl(Fmoc) and triphenylmethyl(Trt) protecting groups and the exchange of thiol-to-disulfide as well. The peptidomimetics holding Trt(3 and 4) showed no gel performance, while the Fmoc groups promoted 5 and 6 to give rise to thermo-reversible organogels in a number of organic solvents. The self-assembled fibrillar networks were distinctly evidenced in the organogels by transmission electron microscopy(TEM) and scanning electron microscopy(SEM) observations. Fourier transform infrared spectroscopy(FT-IR) and fluorescence analyses revealed that the hydrogen bonding and ?-? stacking play as major driving forces for the self-assembly of these organogelators. A ?-turn secondary structure was deduced for the organogel of 6 by virtue of X-ray diffraction, FT-IR and circular dichroism(CD) measurements, and an interdigitated bilayer structure was also presented.     

Boc或Cbz保护的L-脯氨醇衍生物的稳定性

近年来,L-脯氨醇衍生物催化的不对称Michael加成反应已经成为手性催化研究领域的热点.而在L-脯氨醇衍生物的合成中,常常涉及到L-脯氨醇氨基的保护.为此,研究了Boc和Cbz保护的脯氨醇衍生物的稳定性,发现Boc保护的L-脯氨醇在羟基被取代为易离去基团时,就变得不稳定,在67℃就发生分子内环合生成化合物y-丁内酯;而Cbz保护的L-脯氨醇衍生物的稳定性要好得多,在140℃且有三乙胺存在时,才会发生类似的分子内环合反应.     

Interaction of trimethylchlorosilane with silanol groups silica surface in the presence of amines

Experimental and quantum chemical studies of ClSi(CH₃)₃ interactions with SiOH groups catalyzed by amines were carried out using aerosil samples. The catalytic effects are due to the enthalpy factor of rate constants through transition state stabilization by NR₃.     

Rapid and facile Lewis acid catalysed Boc protection of amines

Efficient Boc protection of amines was carried out using (Boc)₂O in the presence of a catalytic amount of ZrCl₄ (10 mol %) in acetonitrile at room temperature. The reaction times are very short and the yields are generally high.