Pentafluorophosphato‐Phenylalanines: Amphiphilic Phosphotyrosine Mimetics Displaying Fluorine‐Specific Protein Interactions

Phosphotyrosine residues are essential functional switches in health and disease. Thus, phosphotyrosine biomimetics are crucial for the development of chemical tools and drug molecules. We report here the discovery and investigation of pentafluorophosphato amino acids as novel phosphotyrosine biomimetics. A mild acidic pentafluorination protocol was developed and two PF₅‐amino acids were prepared and employed in peptide synthesis. Their structures, reactivities, and fluorine‐specific interactions were studied by NMR and IR spectroscopy, X‐ray diffraction, and in bioactivity assays. The mono‐anionic PF₅ motif displayed an amphiphilic character binding to hydrophobic surfaces, to water molecules, and to protein‐binding sites, exploiting charge and H−F‐bonding interactions. The novel motifs bind 25‐ to 30‐fold stronger to the phosphotyrosine binding site of the protein tyrosine phosphatase PTP1B than the best current biomimetics, as rationalized by computational methods, including molecular dynamics simulations.

Side-Chain Modification of Peptides Using a Phosphoranylidene Amino Acid

The flexible variation of peptidomimetics is of great interest for the identification of optimized protein ligands. Here we present a general concept for introducing side-chain modifications into peptides using triarylphosphonium amino acids. Building blocks 4a and 4b are activated for amidation and incorporated into stable peptides. The obtained phosphoranylidene peptides undergo Wittig olefinations and 1,3-dipolar cycloaddition reactions, yielding peptidomimetics with vinyl ketones and 5-substituted 1,2,3-triazoles as non-native peptide side chains.

An Intrinsic Hydrophobicity Scale for Amino Acids and Its Application to Fluorinated Compounds

More than 100 hydrophobicity scales have been introduced, with each being based on a distinct condensed-phase approach. However, a comparison of the hydrophobicity values gained from different techniques, and their relative ranking, is not straightforward, as the interactions between the environment and the amino acid are unique to each method. Here, we overcome this limitation by studying the properties of amino acids in the clean-room environment of the gas phase. In the gas phase, entropic contributions from the hydrophobic effect are by default absent and only the polarity of the side chain dictates the self-assembly. This allows for the derivation of a novel hydrophobicity scale, which is based solely on the interaction between individual amino acid units within the cluster and thus more accurately reflects the intrinsic nature of a side chain. This principle can be further applied to classify non-natural derivatives, as shown here for fluorinated amino acid variants.

Preparation and Reactions of Trichloromethyl-Substituted Pyridine and Pyrimidine Derivatives

The three-component reaction of lithiated methoxyallene, nitriles and trichloroacetic acid gave three model β-keto enamides that were starting materials for the synthesis of trichloromethyl-substituted pyridine and pyrimidine N-oxide derivatives. Upon treatment with acetic anhydride, the methyl group of the prepared pyrimidine N-oxides was converted into an acetoxymethyl group by a Boekelheide rearrangement. A few typical experiments also revealed that the trichloromethyl group of the prepared pyrimidine N-oxides can be replaced by an alkoxy or a hydroxy group, or transformed into an arylthiomethyl group. An alternative approach to β-keto enamides via the corresponding β-keto enamines was also examined and provided the expected 4-hydroxy-6-(trichloromethyl)pyridine derivative in good yield.

Benzyl Mono-P-Fluorophosphonate and Benzyl Penta-P-Fluorophosphate Anions Are Physiologically Stable Phosphotyrosine Mimetics and Inhibitors of Protein Tyrosine Phosphatases

α,α-Difluoro-benzyl phosphonates are currently the most popular class of phosphotyrosine mimetics. Structurally derived from the natural substrate phosphotyrosine, they constitute classical bioisosteres and have enabled the development of potent inhibitors of protein tyrosine phosphatases (PTP) and phosphotyrosine recognition sites such as SH2 domains. Being dianions bearing two negative charges, phosphonates, however, do not permeate membranes and thus are often inactive in cells and have not been a successful starting point toward therapeutics, yet. In this work, benzyl phosphonates were modified by replacing phosphorus-bound oxygen atoms with phosphorus-bound fluorine atoms. Surprisingly, mono-P-fluorophosphonates were fully stable under physiological conditions, thus enabling the investigation of their mode of action toward PTP. Three alternative scenarios were tested and mono-P-fluorophosphonates were identified as stable reversible PTP1B inhibitors, despite of the loss of one negative charge and the replacement of one oxygen atom as an H-bond donor by fluorine. In extending this replacement strategy, α,α-difluorobenzyl penta-P-fluorophosphates were synthesized and found to be novel phosphotyrosine mimetics with improved affinity to the phosphotyrosine binding site of PTP1B.

Plasma anti-mullerian hormone: an endocrine marker for in vitro embryo production from Bos taurus and Bos indicus donors

The aim of this study was to evaluate the association between plasma anti-mullerian hormone (AMH) concentration and in vitro embryo production (IVP) from Bos taurus (Holstein) and Bos indicus (Nelore) donors. A total of 59 Holstein (15 prepubertal heifers aged 8-10 mo, 15 cyclic heifers aged 12-14 mo, 14 lactating cows, and 15 nonlactating cows) and 34 Nelore (12 prepubertal heifers aged 10-11 mo, 10 prepubertal heifers aged 21-23 mo, and 12 cyclic heifers aged 24-26 mo) females were enrolled. All females underwent an ovum pick-up (OPU), without previous synchronization of the follicular wave, and IVP procedure. Immediately before the OPU procedure, blood samples were collected for subsequent AMH determination. A positive correlation was observed between the plasma AMH and number of in vitro embryos produced from Holstein (r = 0.36, P < 0.001) and Nelore (r = 0.50, P = 0.003) donors. For additional analyses, donors within each genotype were classified into 1 of 2 AMH categories (low or high) according to the average AMH concentration for each genotype. The results revealed that females classified as having high AMH presented a greater number of visible aspirated follicles (Holstein: 20.9 ± 1.5 vs 13.6 ± 0.9, P < 0.0001; Nelore: 54.3 ± 6.1 vs 18.6 ± 2.1, P < 0.0001) and a greater number of recovered cumulus-oocyte complexes (Holstein: 17.3 ± 1.5 vs 9.0 ± 0.9, P < 0.0001; Nelore: 45.3 ± 6.4 vs 13.4 ± 1.7, P < 0.0001). However, there was no difference in the blastocyst production rate (Holstein: 20.6% ± 4.0% vs 19.8% ± 4.2%, P = 0.60; Nelore: 33.7% ± 6.5% vs 27.4% ± 5.5%, P = 0.41, high and low AMH, respectively). Moreover, donors classified as having high AMH yielded a greater number of embryos produced per OPU (Holstein: 3.0 ± 0.7; Nelore: 7.0 ± 1.7) compared with those classified as having low AMH (Holstein: 1.2 ± 0.3, P = 0.04; Nelore: 2.2 ± 0.5, P = 0.007). In conclusion, although the plasma AMH concentration did not alter the ability of the cumulus-oocyte complex to reach the blastocyst stage, the AMH concentration in plasma can be an accurate endocrine marker for the in vitro embryo yield from either B. taurus (Holstein) or B. indicus (Nelore) donors. Therefore, AMH is a promising tool to enhance the overall efficiency of OPU-IVP programs in the field as a selective criterion for high embryo producing donors.