Vive la différence! Replacement of the base‐linker amide functionality in peptide nucleic acids (PNAs) by an isostructural C−C double bond (shown schematically) leads to a dramatic change in DNA affinity, preferred strand orientation, and triplex‐forming properties, and thus highlights the importance of electrostatic properties over geometric properties of the amide functionality in PNA/DNA recognition.

IntroductionWe report on the preparation and efficacy of 10‐hydroxystearic acid (HSA) that improves facial age spots and conspicuous pores.MethodsThe hydration of oleic acid into HSA was catalyzed by the oleate hydratase from Escherichia coli. Following treatment with HSA, collagen type I and type III was assessed in primary human dermal fibroblasts together with collagen type III, p53 protein levels and sunburn cells (SBC) after UVB irradiation (1 J cm−2) by immunohistochemistry on human ex vivo skin. UVB‐induced expression of matrix metalloprotease‐1 (MMP‐1) was determined from full thickness skin by RT‐qPCR. Modification of the fibroblast secretome by HSA was studied by mass‐spectrometry‐based proteomics. In a full‐face, double blind, vehicle‐controlled trial HSA was assessed for its effects on conspicuous facial pore size and degree of pigmentation of age spots in Caucasian women over an 8‐week period.ResultsHSA was obtained in enantiomeric pure, high yield (≥80%). Collagen type I and type III levels were dose‐dependently increased (96% and 244%; P < 0.01) in vitro and collagen type III in ex vivo skin by +57% (P < 0.01) by HSA. HSA also inhibited UVB‐induced MMP‐1 gene expression (83%; P < 0.01) and mitigated SBC induction (−34% vs. vehicle control) and reduced significantly UV‐induced p53 up‐regulation (−46% vs. vehicle control; P < 0.01) in irradiated skin. HSA modified the fibroblast secretome with significant increases in proteins associated with the WNT pathway that could reduce melanogenesis and proteins that could modify dermal fibroblast activity and keratinocyte differentiation to account for the alleviation of conspicuous pores. Docking studies in silico and EC50 determination in reporter gene assays (EC50 5.5 × 10−6 M) identified HSA as a peroxisomal proliferator activated receptor‐α (PPARα) agonist. Clinically, HSA showed a statistically significant decrease of surface and volume of skin pores (P < 0.05) after 8 weeks of application and age spots became significantly less pigmented than the surrounding skin (contrast, P < 0.05) after 4 weeks.ConclusionHSA acts as a PPARα agonist to reduce the signs of age spots and conspicuous pores by significantly modulating the expression of p53, SBC, MMP‐1 and collagen together with major changes in secreted proteins that modify keratinocyte, melanocyte and fibroblast cell behavior.

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A monomeric unit of a conformationally constrained PNA analog, E-olefinic peptide nucleic acid (E-OPA) containing the base thymine was synthesized in 14 steps. The key step involved a palladium (0) catalyzed cross-coupling reaction utilizing a Reformatsky reagent as nucleophile. A protecting group regime that is compatible with solid-phase PNA and DNA chemistries was chosen.Peptide nucleic acid (PNA), reported in 1991 by Nielsen, 1 is a nucleic acid analog with remarkable pairing properties. Much work has since been invested in understanding and improving this potentially useful analog. 2 Oligomers of PNA are able to form stable duplexes with both DNA and RNA in both antiparallel and parallel orientations. Structural characterizations 3 show that when PNA is complexed with a natural nucleic acid the internal amide bond of the PNA units are uniformly aligned so that the carbonyl oxygen of the tertiary amide bond points to the carboxy terminus in an antiparallel Watson-Crick duplex. Olefinic peptide nucleic acid (OPA) monomers were designed as PNA analogs with an internal olefin of defined configuration. We reasoned that the replacement of the conformationally labile amide bond with a conformationally rigid olefin bond would allow an assessment of the role of this preorganized structural element in the duplex binding orientation observed in PNA (Scheme 1). From structural models, we anticipate that the Z-OPA isomer will bind in a parallel fashion, while the E-OPA isomer will bind in an anti-parallel orientation. The synthesis of a Z-OPA monomer has already been reported, 4 herein we report the synthesis of the thymine containing E-OPA monomer.The syntheses of OPA monomers were designed to be divergent, with both E and Z-isomers utilizing a common intermediate 1 (Scheme 2). The E-isomer is then obtained using functional group interconversion to reverse the amino acid polarity and introduce the correct nucleobase(s). The basic OPA skeleton 1 is assembled from the vinyl iodide via a palladium(0) catalyzed cross-coupling reaction utilizing an ethyl a-bromoacetate derived Reformatsky reagent as the nucleophile. 5 The geometry of the olefin is defined via a stereospecific conversion of the propargyl alcohol to the Z-iodo olefin. 6 In anticipation of assembly of this monomer into oligomers utilizing solid-phase synthesis, a strategy incorporating the monomethoxytrityl amino protecting group and acyl base protection was chosen. 7 This system was selected over the standard PNA (and peptide) chemistries due to the need to avoid strongly acidic conditions which would scramble the double-bond position and geometry. Furthermore, this strategy is compatible with DNA synthesis chemistry, allowing us to construct DNA/OPA chimeras.The synthesis of the thymine E-OPA amino acid 10 was begun from commercially available 3-butynol 2 (Scheme 3). The alcohol was protected as the THP acetal followed Scheme 1Downloaded by: Queen's University. Copyrighted material.