Hydrophilic/hydrophobic patterning is a well-established design strategy to guide secondary structure formation of both natural as well as non-natural oligomers and polymers. This contribution explores the feasibility of a new approach for the synthesis of uniform, sequence-defined, hydrophilic/ hydrophobic patterned oligo(α-hydroxy acid)s. The proposed strategy is based on post-modification of a reactive oligoester scaffold composed of an alternating sequence of hydrophobic [(2S)-2-hydroxy-4-methylpentanoic acid] and masked hydrophilic [(2S)-2-hydroxypent-4-enoic acid] α-hydroxy acids. The use of (2S)-2-hydroxypent-4-enoic acid instead of a complex side-chain-protected hydrophilic building block obvi-
This contribution explores different strategies for the synthesis of side chain functional polydepsipeptides. First, the ring‐opening polymerization of side chain functional morpholine‐2,5‐diones is revisited and the optimized reaction conditions used for the polymerization of (Z)‐L‐Lys, (Boc)‐L‐Lys and L‐allylglycine based morpholine‐2,5‐diones. As a first approach towards side chain functional polydepsipeptides, the deprotection of poly(Glc‐alt‐(Z)‐L‐Lys) and poly(Glc‐alt‐(Boc)‐L‐Lys) is evaluated. Although under appropriate conditions, the side chain protecting groups can be quantitatively removed, the reaction conditions used here were found to lead to backbone degradation. As an alternative approach, the thiol‐ene post‐polymerization modification of poly(Glc‐alt‐allylglycine) is explored. Free radical addition of various ω‐functional thiols was found to proceed without backbone degradation and in several cases with quantitative allyl group conversion. The post‐polymerization modification strategy is attractive as it obviates the need for protecting group chemistry and facilitates the synthesis of diverse libraries of side chain functional polydepsipeptides.
Hydrophilic/hydrophobic patterning is a powerful strategy to control folding in non-natural polymers/oligomers. In this contribution, we present a novel strategy for the preparation of alternating hydrophilic/hydrophobic patterned non-natural peptide foldamers. This strategy relies on the post-modification of a reactive peptide precursor that can be prepared via standard solid phase peptide synthesis without the need for side chain protective groups. The peptide scaffolds consisted of an alternating sequence of l-leucine and l-allylglycine residues. Using thiol-ene chemistry, the double bonds in the side chains of the l-allylglycine units could be post-modified with cysteamine hydrochloride, thioglycolic acid, 1-thioglycerol or 2,3,4,6-tetra-O-acetyl-thio-beta-d-glucopyranose to afford alternating hydrophilic/hydrophobic patterned peptides. In agreement with the alternating hydrophilic/hydrophobic patterned primary structure, cysteamine and thioglycolic acid post-modified octapeptides were found to adopt a beta-sheet secondary structure in basic or acidic aqueous media, respectively. The proposed synthetic approach is not only of interest to generate diverse libraries of peptide foldamers from a limited number of reactive precursor scaffolds, but may also represent an attractive, general strategy for the synthesis of peptides with complex side chain functionalities that are not easily accessible via standard solid phase techniques.
BACKGROUND: Calcific aortic valve disease (CAVD) is characterized by a phenotypic switch of valvular interstitial cells to bone-forming cells. Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors at the interface between innate immunity and tissue repair. Type I interferons (IFNs) are not only crucial for an adequate antiviral response but also implicated in bone formation. We hypothesized that the accumulation of endogenous TLR3 ligands in the valvular leaflets may promote the generation of osteoblast-like cells through enhanced type I IFN signaling. METHODS: Human valvular interstitial cells isolated from aortic valves were challenged with mechanical strain or synthetic TLR3 agonists and analyzed for bone formation, gene expression profiles, and IFN signaling pathways. Different inhibitors were used to delineate the engaged signaling pathways. Moreover, we screened a variety of potential lipids and proteoglycans known to accumulate in CAVD lesions as potential TLR3 ligands. Ligand-receptor interactions were characterized by in silico modeling and verified through immunoprecipitation experiments. Biglycan ( Bgn ), Tlr3 , and IFN-α/β receptor alpha chain ( Ifnar1 )–deficient mice and a specific zebrafish model were used to study the implication of the byglycan (BGN)-TLR3-IFN axis in both CAVD and bone formation in vivo. Two large-scale cohorts (GERA [Genetic Epidemiology Research on Adult Health and Aging], n=55 192 with 3469 aortic stenosis cases; UK Biobank, n=257 231 with 2213 aortic stenosis cases) were examined for genetic variation at genes implicated in BGN-TLR3-IFN signaling associating with CAVD in humans. RESULTS: Here, we identify TLR3 as a central molecular regulator of calcification in valvular interstitial cells and unravel BGN as a new endogenous agonist of TLR3. Posttranslational BGN maturation by xylosyltransferase 1 (XYLT1) is required for TLR3 activation. Moreover, BGN induces the transdifferentiation of valvular interstitial cells into bone-forming osteoblasts through the TLR3-dependent induction of type I IFNs. It is intriguing that Bgn −/− , Tlr3 −/− , and Ifnar1 −/− mice are protected against CAVD and display impaired bone formation. Meta-analysis of 2 large-scale cohorts with >300 000 individuals reveals that genetic variation at loci relevant to the XYLT1–BGN–TLR3–interferon-α/β receptor alpha chain (IFNAR) 1 pathway is associated with CAVD in humans. CONCLUSIONS: This study identifies the BGN-TLR3-IFNAR1 axis as an evolutionarily conserved pathway governing calcification of the aortic valve and reveals a potential therapeutic target to prevent CAVD.
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