Bifunctional chiral dehydroalanines for peptide coupling and stereoselective <i>S</i>-Michael addition

A second generation of chiral bicyclic dehydroalanines easily accessible from serine has been developed. These scaffolds behaved as excellent S-Michael acceptors when tri-O-acetyl-2-acetamido-2-deoxy-1-thio-α-d-galactopyranose (abbreviated as GalNAc-α-SH) was used as a nucleophile. This addition proceeds with total chemo- and stereoselectivity, complete atom economy, quickly, and at room temperature, making it a true click reaction. The Michael adducts were easily transformed into S-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-l- and -d-cysteines, which can be regarded as mimics of the Tn antigen derived from l-Ser (α-d-GalNAc-l-Ser) and d-Ser (α-d-GalNAc-d-Ser), respectively.Peer Reviewe

The use of complementary and alternative medicines among patients with locally advanced breast cancer – a descriptive study

BACKGROUND: Complementary and alternative medicine (CAM) use is common among cancer patients. This paper reviews the use of CAM in a series of patients with locally advanced breast cancer (LABC). METHODS: Women with LABC attending a specialist clinic at a single Canadian cancer centre were identified and approached. Participants completed a self-administered survey regarding CAM usage, beliefs associated with CAM usage, views of their risks of developing recurrent cancer and of dying of breast cancer. Responses were scored and compared between CAM users and non-users. RESULTS: Thirty-six patients were approached, 32 completed the questionnaire (response rate 89%). Forty-seven percent of LABC patients were identified as CAM users. CAM users were more likely to be younger, married, in a higher socioeconomic class and of Asian ethnicity than non-users. CAM users were likely to use multiple modalities simultaneously (median 4) with vitamins being the most popular (60%). Motivation for CAM therapy was described as, "assisting their body to heal" (75%), to 'boost the immune system' (56%) and to "give a feeling of control with respect to their treatment" (56%). CAM therapy was used concurrently with conventional treatment in 88% of cases, however, 12% of patients felt that CAM could replace their conventional therapy. Psychological evaluation suggests CAM users perceived their risk of dying of breast cancer was similar to that of the non-Cam group (33% vs. 35%), however the CAM group had less severe anxiety and depression. CONCLUSION: The motivation, objectives and benefits of CAM therapy in a selected population of women with LABC are similar to those reported for women diagnosed with early stage breast cancer. CAM users display less anxiety and depression and are less likely to believe they will die of their breast cancer. However the actual benefit to overall and disease free survival has yet to be demonstrated, as well as the possible interactions with conventional therapy. Consequently more research is needed in this ever-growing field

Fluorescent amino acids as versatile building blocks for chemical biology

Fluorophores have transformed the way we study biological systems, enabling non-invasive studies in cells and intact organisms, which increase our understanding of complex processes at the molecular level. Fluorescent amino acids have become an essential chemical tool because they can be used to construct fluorescent macromolecules, such as peptides and proteins, without disrupting their native biomolecular properties. Fluorescent and fluorogenic amino acids with unique photophysical properties have been designed for tracking protein–protein interactions in situ or imaging nanoscopic events in real time with high spatial resolution. In this Review, we discuss advances in the design and synthesis of fluorescent amino acids and how they have contributed to the field of chemical biology in the past 10 years. Important areas of research that we review include novel methodologies to synthesize building blocks with tunable spectral properties, their integration into peptide and protein scaffolds using site-specific genetic encoding and bioorthogonal approaches, and their application to design novel artificial proteins, as well as to investigate biological processes in cells by means of optical imaging. [Figure not available: see fulltext.]

Potassium Arylethynyltrifluoroborate as an Unstrained Dienophile for Ultrafast and On Demand Activation of Bioorthogonal IEDDA Reactions

Strained alkenes and alkynes are the predominant dienophiles used in inverse electron-demand Diels-Alder (IEDDA) reactions, however, their instability, cross-reactivity and accessibility are problematic. Unstrained dienophiles, although physiologically stable and synthetically accessible, react with tetrazines significantly slower relative to strained variants. Here we report the development of potassium arylethynyltrifluoroborates as unstrained dienophiles for ultrafast, chemically triggered IEDDA reactions. By varying the substituents on the tetrazine (e.g. pyridyl- to benzyl-substituents), cycloaddition rates can vary from nearly spontaneous (t1/2≈ 9 s) to no reaction with the unstrained alkyne-BF3 dienophile. The reported system was applied to protein modification and enabled mutually orthogonal labelling of two distinct proteins.</p

Towards enantiomerically pure β-seleno-α-amino acids via stereoselective Se-Michael addicions to chiral dehydroalanines

Selenium plays a crucial role in different biological processes, being necessary for theproper functioning of the human body. Therefore, selenium compounds have becomemolecules of great interest due to their antiviral and anticancer activities and their use as naturalfood supplements.Selenocysteine (Sec) is the 21st genetically encoded amino acid and plays an importantrole in protein folding and stability, conferring interesting redox properties. In addition, protectedselenocysteine derivatives are used as precursors of dehydroalanine, which allows theintroduction of various post-translational modifications. On the other hand, some aryl derivativesof Se serve as chemical models for the inhibition of selenoenzymes, which has implications forcancer therapy. Beyond applications in bioconjugation, selenoamino acids are especiallyrelevant in Native Chemical Ligation (NCL).[1]Although the nucleophilic substitution reaction has been widely employed for thesynthesis of these Sec derivatives, 1,4-conjugate addition has been less explored, especiallythe stereoselective 1,4-conjugate addition of Se-nucleophiles to chiral Michael acceptors.Therefore, in this work, we aim to extend the methodology established by our research group[2]to the synthesis of enantiomerically pure selenoamino acids. The key step of such synthesis isthe attack of different Se-nucleophiles to a chiral dehydroalanine, to obtain a singlediastereoisomer. The methodology is simple and does not require the use of any catalyst,providing excellent yields at room temperature. Subsequent facile acid hydrolysis of the abovediastereoisomers leads to the corresponding selenoamino acid

A Double Diastereoselective Michael-Type Addition as an Entry to Conformationally Restricted Tn Antigen Mimics

A totally stereocontrolled <i>C</i>-Michael addition of serine-equivalent <i>C</i>-nucleophiles to tri-<i>O</i>-benzyl-2-nitro-d-galactal was used as the key step to synthesize several pyrano­[3,2-<i>b</i>]­pyrrole structures. These scaffolds could be regarded as conformationally restricted Tn antigen mimics, as we have demonstrated by biological assays. The pyranose rings retain their ⁴C₁ chair conformation, as shown by molecular modeling and NMR spectroscopy. The expected bioactivity was established by a competition-tailored enzyme-linked lectin assay using both soybean and Vicia villosa agglutinins as model lectins. The facile described synthetic route and the strategic combination of computational and experimental techniques to reveal conformational features and bioactivity demonstrate the prepared glycomimics to be promising candidates for further exploitation of this scaffold to give glycans for lectin blocking and vaccination