DESCRIPTION: CL-20 is the most energy-dense explosive material.

Our process will offer multiple benefits as compared to the standard CL-20 production processes.

D. Coucouvanis, A. Salifoglou, , A. Simopoulos, A. Kostikas

After the cleavage the sample is analyzed by HPLC as Fmoc protected and free amino sequences are usually well separated in a standard HPLC gradient.

There is a significant increase in interest for CL-20 in a wide variety of applications.

/ Coucouvanis, D.; Salifoglou, A.; Simopoulos, A.; Kostikas, A.

The addition of HOBt to the piperidine solution helps to reduce the formation of aspartimide. Another approach is to introduce the residue preceeding Asp as the Fmoc(Hmb) protected amino acid [67].

Several examples of aspartimide formation during the peptide elongation have been reported, together with the reopening of the aspartimide cycle during the subsequent Fmoc deprotection step, yielding piperidides [64,65,66].


JO - Journal of the American Chemical Society

The latter system is especially suitable for the cleavage of fully protected fragments to be coupled to another fragment in solution, as it eliminates the use of a carboxylic acid in the cleavage step.

RECOMMENDED STANDARD PROCEDURE

A range of cleavage reagents for peptides synthesized on 2-chlorotrityl resin has been described. TFE/AcOH/DCM (1:1:3) has been developed by Barbs [62]. Cleavage is also rapidly attained with 0.5% TFA/DCM as well as with HFIP/DCM (1:4 or 3:7) [63].

JF - Journal of the American Chemical Society

In peptide synthesis diketopiperazine formation is a notorious side-reaction at the dipeptide stage and is particularly prone to occur in Fmoc based SPPS because of its mechanism.

RECOMMENDED STANDARD PROCEDURE

Filtrates containing sulfur scavengers have to be oxidized to eliminate the pervasive obnoxious smell. For that purpose the TFA filtrate is neutralized (NaOH/ice) before addition of an oxidant (e.g. bleach or a saturated solution of iodine in ethanol).

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A growing proportion of scavengers means reduction of the amount of TFA, thus, cleavage with cocktails containing a considerable amount of scavenger or many different scavengers may take longer.

RECOMMENDED STANDARD PROCEDURE

Sample and bulk cleavages should be performed in a well ventilated hood and protective equipment (gloves, goggles, mask if necessary) worn by the personnel performing the operation.

Determination of the Completion of Fmoc Cleavage

In the development of the cleavage conditions it is also advisable to perform a simultaneous time course evaluation of the evolution of the cleavage. It should be complete in 2-3 hours at room temperature in order to minimize side reactions arising from long exposure to strong acid environment.