Cleavage mixtures

The Hoc group was developed for tryptophan protection to minimize alkylation during BOC-mediated peptide synthesis. It is introduced with the chloroformate (NaOH, CH2CI2, Bu4N HS04 ) and can be cleaved with HF without the need to include thiols in the cleavage mixture. 

Remove the TFA-scavenger mixture, combine it with the first cleavage mixture, and place the tube on ice. 

For precipitation of the peptide add the cold cleavage mixture to 8 mL of ice cold diethyl ether. 

Gramicidin A, however, is attacked by JV -bromoacetamide (NBA) and N-bromosuccinimide (NBS) (Gross and Witkop, unpublished observation). In 50 % aqueous ethyl alcohol at room temperature 5 % of the peptide bonds (20% of the tryptophyl peptide bonds) are cleaved with NBS. Methyl alcohol must be avoided because it opens the spirodioxindole lactone from oxidized tryptophan to the ester even at room temperature. The cleavage mixture separates on electrophoresis (pH = 2.5, sodium-formate buffer) into four ninhydrin-positive components of which the fastest migrating one was identified as ethanolamine. Dinitrophenylation showed leucine and alanine to be additional NHs-terminals of the released fragments. 

Add the ice-cold reagent (15 mL, prepared as in Section 4.3.5.2.1) to the peptide-resin (1.0 g) and mix at 0°C for Ih. All blocking groups used in Fmoc synthesis should be removed during this time, including Arg(Mtr). Work up the cleavage mixture as in the previous section (Section 4.3.5.2.3).0 1... 

After creating positive pressure at the bottom, a cleavage reagent is dehvered to the top plate, which contains all the resins with the synthesized peptides. Upon completion of the cleavage, a vacuum is applied and the filtrates are collected in the 96 deep well collection plate at the bottom. The collection plate is then placed in a vacuum centrifuge to eliminate the cleavage mixture. 

The resin-bearing (272) was dried, and cleavage was performed with 1% TFA in DCM for 15 min. After evaporation of the cleavage mixture, tert-butanol/water 4 1 (v/v) was added. This solution was freeze-dried to obtain the desired product. 

The filtrate from the cleavage reaction is precipitated in diisopropyl ether-petroleum ether (1 1 v/v 20 mL per 1 mL of cleavage mixture) at 0°C, and the precipitate is collected by filtration. 

Description Cumene is oxidized (1) with air at high efficiency (-i-95%) to produce cumene hydroperoxide (CHP), which is concentrated (2) and cleaved (3) under high-yield conditions (-i-99%) to phenol and acetone in the presence of an acid catalyst. The cleavage mixture is neutralized and fractionated to produce high-purity products (4-8), suitable for all applications. AMS is hydrogenated to cumene and recycled to oxidation or optionally recovered as a pure byproduct. 

The reactions of V-substituted D-allo epimines with HCl and HI proceeded trans-diaxially in all cases where the biased conformation of the tetrahydropyran ring was maintained. In the reaction, where 4,6-O-benzylidene group was hydrolyzed prior to aziridine-ring cleavage, mixtures of stereoisomers were formed. ... 

The pins were removed from the glove bag, rinsed with DMF, DMF/H2O, Me-OH, (air-dried) and CH2CI2 and cleaved from the support by immersion in 85 10 5 (v/v) TFA/dimethylsulfide/H20 for 24 h. For benzodiazepine derivatives incorporating tryptophan, 85 5 5 5 (v/v) TFA/dimethyl sulfide/H20/l,2-ethanediol was employed as the cleavage mixture. 

A number of universal cleavage mixtures have been advocated, the most popular of which are Reagent K (TFA/thioanisole/water/phenol/EDT ffi.5 5 5 5 2.5 v/v) and Reagent R (TFA/thioanisole/anisole/EDT 90 5 3 2 v/v) (58). However, with recent developments in protecting group chemistry, in... 

Transfer the cleavage mixture to an appropriate sized round-bottomed flask. 

Carry out steps 1-3 of Protocol 17A, or add the TFA solution (he. cleavage mixture) directly to a 10-fold volume of cold ether. 

The allyl ester protection offers a similar approach (86-88) to that of OTmse esters. However, its removal requires the use of a complex cleavage mixture typically Pd(PPh3)-DMSO-THF-0.5 M aqueous HCl-4-methyl-morpholine over 2 h (89). Care must be taken as the deprotection mixture is hazardous and air sensitive. It should be noted that Protocols 20 and 21 outlined below can be applied for the on-resin deprotection of the N-Alloc group. 

With the exception of lysine, the process of trityl group removal from the side-chains of these amino acids is an equilibrium. Consequently, in order to push the equilibrium in the desired direction, a cation scavenger such as triisopropylsilane (TIS) or 1,2-ethanedithiol (EDT) is added to the cleavage mixture, or the reaction is conducted in a continuous-flow manner. With the latter approach, the progress of the reaction can be monitored at 400-500 nm and by following the decrease in optical density with time of the reaction effluent. 

Prepare Af x 2 ml of cleavage mixture, where N is the number of peptides to be cleaved, each containing 95% trifluoro-... 

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