Unprotected peptides as building blocks for branched peptides and peptide dendrimers

Abstract

We describe two new site‐specific ligation methods for preparing branched peptide dendrimers such as multiple antigen peptide (MAP). Both methods are based on the general approach of exploiting the specific reaction between a weak base and an aldehyde under acidic conditions so that unprotected peptides can be used as building blocks. A weak base such as benzoyl hydrazine or 1,2‐amino thiol of cysteine was attached to the N‐terminal of an unprotected peptide as nucleophile to react with the alkyl aldehyde on the core matrix of MAP to form a stable hydrazone linkage or a five‐membered thiazolidine ring, respectively. Two synthetic peptides rich in basic amino acids such as lysine and arginine were used as models in the ligation reactions in solution to give peptide dendrimers containing four or eight copies of peptide immunogens. The resulting macromolecules with the MW ranging from 5 to 16kDa were unambiguously characterized by laser‐desorption mass spectrometry. Furthermore, we also optimized the conditions of these ligation reactions using elevated temperature and a water‐miscible organic co‐solvent to give a combination of rate enhancement about 10 fold. These optimizations allowed the ligation reactions to be completed in <4h instead of 2–3 days. Our ligation approach also has the advantages of flexibility so that peptides can be attached through the amino or carboxyl terminus to the core matrix. The phenyl hydrazone linkage and the five‐membered ring were found to be stable at physiological pH suitable for immunization. Thus our results provide two practical and useful methods for the synthesis of macromolecular peptide dendrimers for vaccines, artificial proteins and enzymes. © Munksgaard 1995.

Designing Dendrimers for Drug Delivery and Imaging: Pharmacokinetic Considerations

“…These properties have been reported to be closely associated with biocompatibility, biodistribution, and pharmacokinetic characteristics (15)(16)(17)(18), as will be discussed in this review. A vast number of dendrimers have been designed with structural difference used in biological applications, including polyamidoamines (PAMAM) (6), polypropyleneimines (PPI) (19), polyamides or polypeptides (20), polyester (21), and polymelamine (22) dendrimers. Recently, polytriazole dendrimers synthesized by "click chemistry" (23) and "geometrically disassembling" or degradable dendrimers have been developed for controllable structure cleavage by light, enzymes or single triggering events (24).…”

Thiocarbamate‐linked peptides by chemoselective peptide ligation

“…These structures present multiple copies of a particular peptide on a lysine-based core. The synthesis of unambiguous and homogeneous MAPs is usually carried out by ligating chemoselectively purified peptide segments to the lysinyl core peptide presenting the appropriate functional groups at its periphery [18]. Di-and tetravalent lysinyl cores modified by phenylthiocarbonyl groups were synthesized on the solid phase as described in Scheme 6.…”

“…Other methods result in the formation of unnatural covalent bonds such as disulfide [13], oxime [14], hydrazone [15][16][17][18], thioether [13], thiazolidine [18,19], thioester [20] and 1,2,3-triazole linkages [21]. These methods are of great interest when native peptide bonds are not absolutely required.…”

Synthesis of multiple antigenic peptides (MAPs)—strategies and limitations

“…While both approaches have as common requirement a branched poly‐lysine core (see Reaction Scheme), in the direct method each branch is elongated into the corresponding epitope by stepwise SPPS, whereas in the indirect method the core is appropriately functionalized at each branch to give a multivalent platform to which peptide epitopes are chemoselectively tethered. This latter approach has the known theoretical advantage of convergent methods, which allow the pre‐purification and characterization of both core and epitope components5, 6, and thus lead to better‐defined, more unambiguous end‐products than the all‐SPPS direct method, where the simultaneous stepwise growth of multiple peptide chains may act as an amplifier of synthetic errors (deletions, truncations, side reactions) and cause microheterogeneity in the final material. These plausible claims in favor of the conjugation method are unfortunately backed by a rather sparse body of reliable chemical documentation, and thus open to question.…”