Cis-diol -amino acids
Amino acids carrying cis-diol groups are able to mediate bioorthogonal ligation reactions. We study flexible side chains like RbS, monocyclic amino acids like Dyp or bicyclic dipeptides like hot=Tap. These amino acids are either used as single “mutations” in natural peptides (application: enzyme inhibitors), or as scaffolds for the self-assembly of specific oligomers of amyloidogenic peptides (application: synthetic miniamyloids), or in the synthesis of natural products like the dihydroxylated collagen (application: biomineralisation).
The three-letter code of the natural -amino acids corresponds to the three-atom repeat of polypeptide backbones. We apply the three-letter code to all new -amino acids too, to stress the likeness between the backbone register of natural and synthetic -amino acids. A common backbone structure allows the analysis and discussion of conformational properties on the basis of the Ramachandran plot. This concept is easy to understand for the natural amino acids proline Pro, 4-hydroxyproline Hop and 3,4-dihydorxyproline Dyp. In all cases, the three-letter code identifies a single isomer of the two possible stereoisomers of proline, the four of hydroxyproline and the six of dihydroxyproline. A capital first letter distinguishes L-amino acids from D-amino acids which are identified by a small first letter. Dyp is unmistakable an L-amino acid. All six potential stereoisomers of 3,4-dihydroxyproline may be distinguished by the three-letter code with capital and small letters.
D-Ribopyranosyl-L-serin RbS names glycosylated natural amino acid Ser. This side chain modification can be installed on other amino acids too, yielding RbT, RbC, etc where the one-letter code of genetically encoded amino acids becomes part of the name.
Naming of new amino acids becomes more challenging when two amino acids are inseparably mergend to a dipeptide. Instead of a single „-“ between both three-letter codes, we suggested to use a „=“ which identifies the non-standard amide linkage. Dha=Tap was the first dipeptide building block named with the six-letter code. Hot=Tap and hot=Tap are more recent examples. Homooligomeric (hot=Tap)n is easily identified as a polypeptide which is assembled from alternating D- and L- amino acids. This scaffold esterifies spontaneously with peptide-benzoboroxoles in water to form branched peptide oligomers.
Ring-opening polymerization (ROP) of lactones yields polyesters. BICpoly is a synthetic polyhydroxylated polyester which is obtained by regiospecific ROP of the lactone (2).
The crystal structure of the trihydroxylated precursor 2 shows the constrained oligocyclic bridged ring system which is difficult to draw as a Lewis formula.
More details in the publication list.