N-Triazinylammonium Tetrafluoroborates. A New Generation of Efficient Coupling Reagents Useful for Peptide Synthesis

Abstract

A new generation of triazine-based coupling reagents (TBCRs), designed according to the concept of "superactive esters", was obtained by treatment of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium (DMTMM) chloride with lithium or silver tetrafluoroborate. The structure of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium tetrafluoroborate was confirmed by X-ray diffraction. Activation of carboxylic acids by using this reagent proceeds via triazine "superactive ester". The coupling reagent was successfully used for the synthesis of Z-, Boc-, and Fmoc-protected dipeptides derived from natural and unnatural sterically hindered amino acids and for fragment condensation, in 80-100% yield and with high enantiomeric purity. The manual SPPS of the ACP(65-74) peptide fragment (H-Val-Gln-Ala-Ala-Ile-Asp-Tyr-Ile-Asn-Gly-OH) proceeded significantly faster than with TBTU or HATU, as well as the automated SPPS of the same fragment gave a purer product than by using TBTU or PyBOP. The reagent was also demonstrated to be efficient in on-resin head-to-tail cyclization of constrained cyclopeptides, in SPPS synthesis of Aib peptides, and in the synthesis of esters from appropriate acids, alcohols, and phenols. The high efficiency and versatility of this new generation of TBCRs confirm, for the first time, the usefulness of the concept of "superactive esters" in rational design of the structure of coupling reagents.

Cellulose Functionalysed with Grafted Oligopeptides

“…The reagents were found efficient in the synthesis of Z-, Boc, or Fmoc protected chromatographically homogenous dipeptides in 72-91%. Moreover, experiments involving activation of sterically demanding 2-aminoisobutyric acid (Aib) confirmed that an access to the reactive centers of immobilized reagents remains principally unrestricted, although slightly lower yield and purity of respective peptides were noticed in this case [9].…”

“…Inexpensive cellulose is offering high loading potential but concurrently attended by the threat of side reaction of nucleophilic hydroxyl groups. Using relatively inert towards hydroxylic group under ambient conditions triazine coupling reagents it was possible to obtain monofunctional triazine condensing reagents 1 and bifunctional reagent 2 by the treatment of cellulose with 2,4-dichloro-6-methoxy-1,3,5-triazine or cyanuric chloride respectively [3]. An independent approach towards immobilization of cyanuric chloride was confirmed the general utility of this procedure [4].…”

“…When the cleavage is carried out with nucleophils in an anhydrous environment, the substitution of the ester bond leads to amides, hydrazides and other derivatives. Further stages of the synthesis included the standard SPPS conditions: deprotections of Fmoc group and subsequent condensation with Fmoc/tBu-protected amino acids by using DMT/NMM/BF4 as a coupling reagent [76]. The data summarized in Table 3 shown that in the several cases for the same antigen the strengths of reaction with antibody depends on the anchoring method.…”

“…Another approach to the synthesis of peptides attached to the cellulose matrix within Nterminus and presenting free C-terminus [85] was based on the utilization of 1,3,5-triazine derivative as an anchoring group. The peptides anchored via N-terminal moiety to the cellulose plate, were synthesized in accord to step-by-step methodology by means of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium tetrafluoroborate (DMT/NMM/BF4) as a coupling [86]. 2-Chloro-1,3,5-triazine fragment, used as an anchoring group, was introduced by the treatment of cellulose with 2,4-dichloro-6-methoxy-1,3,5-triazine (DCMT) [87].…”

“…For the standard laboratory Whatman filter paper, typical anchoring of triazine condensing reagent gave density of loading 0.6 -1.0*10 -6 mmole/cm 2 . An expedient matrix for the preparation of indexed library of amides and oligopeptides has been obtained by the demarcation of the surface of the cellulose plates chess-wise by the thin lines imprinted by polysilane, allocated separated, squared area for parallel synthesis of each individual compound (flat reactors) [5]. Application of carboxylic components into compartments of the matrix afforded "superactive" [6] triazine esters 3 linked to the support.…”