Coupling yield

When the Dnseoc group is used in nucleoside synthesis, the coupling yields are determined by measuring the absorbance at 350 nm of each eluate from the Dnseoc-deprotection steps containing the 5-(dimethylamino)naphthalene-l-yl-vinyl sulfone or by measuring the fluorescence at 530 nm. ... 

Reducing agent Coupling yield Temperature Reference... 

Whereas in the case of 72 the coupling yield is 38 % (82% per coupling step), in the case of the butadiynes the yield of 71 drops to 11 % (64% per step). The generally lower yield of the cymantrenes in these couplings has to do with the enhanced steric crowding in 70 as compared to 62, a fivefold instead of a fourfold coupling, and the presence of a larger n-face, which is more prone to react with the active Pd-species in an unwanted fashion. 

Wash the activated particles 3 times with anhydrous THF to remove excess CDI and reaction by-products. After the final wash, remove the solvent and perform a quick wash with ice-cold water to remove most traces of solvent in the particle pellet. Finally, resuspend the particles at 10 mg/ml in cold 0.1 M sodium phosphate, pH 8.2, or 0.1 M sodium carbonate, pH 9.5 (coupling buffer). The higher pH coupling buffer will result in greater reactivity of the imidazole carbamate and greater coupling yields for proteins. 

React at room temperature for up to 3 days (or at 4°C, if the protein is not stable at ambient temperature). The optimal time of reaction is dependent on the protein being coupled and the number of alkyne reactive groups available. An alkynyl-protein added to the nanoparticles at a high molar ratio probably would reach maximal coupling yield in a matter of hours. 

For a more representative investigation, the authors synthesized a fragment of the acyl carrier protein (6S 74ACP) using preformed active esters in N,N-dimethyl-formamide [22]. Each coupling step required only 4 min of irradiation in a modified domestic oven with an average coupling yield of >99% (Scheme 7.2). 

Related alkyne couplings yield tricyclic quinolines via a regioselective amination/C-H functionalization pathway (Equations (104) and (105)).98... 

Zhang236 has also reported a Pd(0)-catalyzed cyclization-arylation cascade of 1,6-enynes that proceeds via the formation of a 7r-allylpalladium intermediate and the subsequent Suzuki coupling, yielding adducts with stereo-defined exocyclic double bonds (Scheme 60). 

In addition, arylthiophene 70 was obtained by a one-pot Suzuki coupling of p-methoxyiodobenzene and 3-bromothiophene via an in situ boronate formation using one equivalent of the thermally stable diborane 69 [55], This method avoids the isolation of boronic acids and is advantageous when base-sensitive groups such as aldehyde, nitriles and esters are present. However, the cross-coupling yields are low when both aryl halides are electron-poor because of competitive homocoupling during the reaction. 

The synthesis and application of glycosyl dimethylthiophosphate donors has also been reported.52 These donors were prepared from the reducing sugars in moderate to good yield and exhibit considerable shelf stability. Glycosylation reactions with a variety of primary and secondary glycosyl acceptors suffered from poor stereoselectivity and required silver triflate as promoter to achieve reasonable coupling yields (Scheme 6.16). 

H Hagenmeier, H Frank. Increased coupling yields in solid phase peptide synthesis with a modified carbodiimide coupling procedure. Hoppe-Seyler s Z Physiol Chem 353, 1973, 1972. 

A completely different tactic is the use of microwave energy absorption of this energy by a peptide results in decreased aggregation. Lithium salts facilitate the solution of peptides in these polar solvents, increase the rate of swelling of polar resins, and improve coupling yields. Sometimes the order of addition of two solvents to a peptide makes a difference. The inclusion of pyridine can also have a beneficial... 

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