Thiol-reactive functions

A frequently used strategy to couple peptides to the surface of liposomes consists in the use hydrophobic/amphipathic anchors that are functionalized with maleimide or bromoacetyl groups, i.e., thiol-reactive functions, which give by reaction with HS-peptides very stable thioether linkages. These functions are conveniently introduced into hydrophobic anchors such as phospholipids, e.g., PE (9,10), the adjuvant PamsCAG (11) or cholesterol... 

The two examples from our work we are going to describe below are the design and study of liposomal diepitope constructs combining either (i) B and T-helper (Th) peptide epitopes, which induced particularly powerful humoral responses (21) (Fig. 3) or (ii) CTL and Th epitopes, which provided a powerful antitumor vaccine (74) (Fig. 4). For the production of these constructs we have conjugated peptides that contain a cysteine residue either at the N- or C-terminus, to the surface of preformed liposomes by reaction with thiol reactive functionalized phospholipids and/or PamaCys lipopeptide anchors (Fig. 2). To that end, we have developed strategies that give, in aqueous media, high... 

Both thiol-derivatized peptides were conjugated to the surface of small unilamellar vesicles (PC/PG/Chol 75/20/50 65nm dia.) containing a thiol-reactive functionalized PamsCSS anchor (11,59), i.e., an amphipathic triacylated lipopeptide chosen for its adjuvanticity, its activation of DCs... 

Noy J-M, Koldevitz M, Roth PJ (2015) Thiol-reactive functional poly(melh)actylales multicomponent monomer synthesis, RAFT (co)polymerization and highly efficient thiol-para-fluoro postpolymerization modification. Polym Chem 6 436-447... 

To synthesize linear polymers, a feasible strategy is to click one molecule with dithiol functionalities and another molecule with two thiol-reactive functionalities such as diene together as shown in Figure 8.2. 

Figure 8.2 Synthesis of linear polymers by polymerizing dithiol and molecules with two thiol-reactive functionalities.

Thiol functionality Thiol-reactive functionality 000030 Polymer chain... 

Figure 7.10 An NHS-PEG-maleimide compound can be used to functionalize dendrimers to provide a hydrophilic spacer terminating in thiol-reactive groups. Thiol-containing proteins then can be conjugated to this reactive intermediate to form covalent thioether bonds.

A special form of homofimctional hnking utihzes so called dendrimers. Dendrimers are nanospherical structures for which the exact size depends on the number of branching points and which carry reactive functional units in their periphery (for example aldehyde-, thiol-, epoxy groups etc). The structure of dendrimers is similar to a tree, and their ramifications consist of repetitive units. It should be noted that their size is limited due to the fact that the packing density of their terminal groups increases. With increasing size, their macroscopic structure approximates the form of a sphere. 

Thioesters are more reactive towards nucleophilic substitution than oxygen esters, and are widely employed in natural biochemical processes because of this property. Coenzyme A is a structurally complex thiol, and functions in the transfer of acetyl groups via its thioester acetyl coenzyme A (acetyl-CoA CH3CO-SC0A). 

The reactivity of halogen compounds, of course, strongly depends on the halogen. Fluoroaliphatic compounds are nonreactive unless they contain another reactive functional group. Chloro-compounds are fairly reactive, k > 108 M 1 s 1, and their reactivity increases in the presence of neighbouring electron withdrawing groups. Bromo-and iodo-compounds are more reactive in that order. Thiols and disulphides are very reactive, whereas thiol anions and thioethers are only fairly reactive. Nitro- and nitroso-compounds are very reactive toward eaq. 

The preparation of disulfide-stabilized nanogel PEG/DNA complexes with a diameter of around 100 nm was reported by Mok et al. [128], A thiol-functionalized six-arm branched PEG was used for DNA solubilization in DMSO, which led to spontaneous PEG/DNA nanocomplex formation. Subsequent addition of the thiol-reactive dithio-bis-maleimidoethane (DTME) disulfide crosslinker led to stabilized nanogels (Fig. 6) that showed high gene transfection efficiency. 

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