Solution-phase synthesis, lipidated peptides

Figure 4 Sequences of lipidated peptides discussed in this review. The frizzled lines Indicate the building blocks used for the block coupling strategy of the solution-phase synthesis (when applicable). Abbrevations BiotAca N-(+)-Biotinyl-6-aminocaproyl MantAca N-methylanthranyl-6-aminocaproyl MIC 6-Maleimidocaproyl NBDAca N-(4-nitrobenz-2-oxa-l, 3-diazol-7-yl)-6-aminocaproyl.

Considering all these features and limitations, it is understandable that currently there is no general procedure available, such as the Fmoc or Boc protocols that are available for nonfunctionalized peptides. However, several approaches have been developed in the last two decades to make lipidated peptides accessible. This chapter describes both the corresponding solution-phase approaches and solid-support approaches for the synthesis of lipidated peptides. In line with the framework sketched above, both the different protecting groups and solid-phase linker systems that have been developed will be reviewed. 

By analogy to the solution-phase approaches, the introduction of lipid functionalities on peptides on the solid support can also follow two general approaches, either using prelipidated building blocks in the standard solid-phase peptide synthesis or via selective lipidation on resin. " " ... 

For such an integrated research activity, differently modified peptides and proteins that carry modifications whose structure can be changed at will through synthesis are invaluable tools. Therefore, the synthesis of the lipidated peptides is an important theme. Lipidated peptides can typically not be accessed via standardized peptide synthesis methods. However, employing the synthetic tools developed and presented here, most types of lipidated peptides can now be synthesized and obtained in pure form. Even though solution-phase approaches still play a significant role in the synthesis of lipidated peptides, the recently developed solid-phase synthesis methods delineate the preferred strategy to access the majority of the required lipidated peptides. 

Introduction of lipid functionalities into peptides can follow two general strategies, independent of solid-phase or solution-phase chemistry. Either the lipid groups are introduced via coupling of prelipidated amino acids to the peptide (Fig. 3a) or they are introduced via selective lipidation of a peptide (Fig. 3b-e). Both the use of prelipidated building blocks (14-16) and of resin lipidation (17-25) have been investigated for the synthesis of lipidated peptides on solid support. 

Here, both solution-phase approaches and solid-phase approaches undertaken for the synthesis of specific lipidated peptides are reviewed (Fig. 4). For the solution-phase approaches, the focus is on the coupling strategy applied, i.e., which block couplings were pursued. The solid-phase approaches are reviewed with the focus on the type of linker to be used for specific types of lipidated peptides. 

A large body of work has been devoted to the synthesis of the C -terminal lipidated peptides of the small GTPases H-/N-Ras. As such, these peptides have been synthesized in solution, via combined solution and solid support approaches and completely on solid phase. 

Synthesis of Lipidated Peptides by Combined Solution/Solid-Phase Approach 152... 

As an alternative approach to solution-state NMR methods, which are ineffective with lipid bilayer samples, solid-state NMR methods have been refined sufficiently to permit structural details to be obtained for membrane-embedded peptides and proteins. This usually requires isotopic enrichment, either through chemical synthesis or biosynthetic incorporation in expressed peptides and proteins. In the absence of routine X-ray crystallographic structural studies for these molecules, solid-state NMR spectroscopy has the potential to be a powerful and unique approach to determining the structures and describing the dynamics and functions of membranes and membrane-bound proteins. In addition, solid-state NMR spectroscopy has been widely used to describe lipid structure, dynamics and phase properties. Thus, solid-state NMR experiments can be... 

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