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Significant efforts have been made in recent years to identify more environmentally benign and less hazardous alternatives to N,N-dimethylformamide (DMF) in solid-phase peptide synthesis (SPPS). Several greener solvents have been endorsed as suitable candidates yet finding a neat solvent that fully matches the qualities of DMF in SPPS has proven challenging. To this end, we recently demonstrated that green binary solvent mixtures are viable alternatives to DMF and showed that the polarity and viscosity profile of a binary solvent mixture can be used to predict its utility in SPPS. In this report, we systematically investigate how the composition of green binary solvent mixtures influences Fmoc-removal, peptide coupling and common side-reactions in SPPS and show that the purity profile is not impacted adversely in binary solvent mixtures when compared to DMF. Furthermore, we demonstrate that the sole variation of the composition of the binary solvent mixture during synthesis represents a novel and simple tool to mitigate certain side-reactions in SPPS, exemplified by suppression of Arg-lactamisation and aspartimide formation. When applied to the synthesis of the peptide therapeutic Bivalirudin on a 7.5 mmol scale, we showed that simply adjusting the solvent ratio in a single step of the synthesis significantly suppressed a problematic Arg-lactamisation side-reaction. These results underline that green binary solvent mixtures not only can replace DMF in SPPS but also provide novel solutions for mitigating common side-reactions in SPPS. [ABSTRACT FROM AUTHOR]

Solid-phase peptide synthesis (SPPS) enables routine synthesis of virtually any type of peptide sequence and is the preferred method for peptide synthesis in academia and the pharmaceutical industry alike. Still, SPPS typically requires significant amounts of hazardous solvents and thus suffers from a negative environmental footprint. Such drawbacks have spurred numerous initiatives for solvent substitution, reduction and recycling, and a handful solvents have recently been proposed as potential green alternatives to N,N-dimethylformamide (DMF). In this report, we recognise solvent viscosity and polarity in combination as key physicochemical parameters for SPPS and identify green binary solvent mixtures of dimethyl sulfoxide (DMSO) and 1,3-dioxolane or 2-methyl tetrahydrofuran that closely resemble DMF. In a series of reagent dissolution, resin swelling, peptide coupling and Fmoc-removal experiments we show that combining solvents offers unprecedented opportunities to predict and fine-tune the overall solvent properties for different aspects of SPPS. Lastly, the identified green binary solvent mixtures were employed for the synthesis of a range of challenging model peptides and peptide therapeutics on meaningful scale, demonstrating that binary solvent mixtures are viable green alternatives to DMF in SPPS. [ABSTRACT FROM AUTHOR]

A series of G s protein peptidomimetics were designed and synthesised based on the published X-ray crystal structure of the active state β 2 -adrenergic receptor (β 2 AR) in complex with the G s protein (PDB 3SN6). We hypothesised that such peptidomimetics may function as allosteric modulators that target the intracellular G s protein binding site of the β 2 AR. Peptidomimetics were designed to mimic the 15 residue C-terminal α-helix of the G s protein and were pre-organised in a helical conformation by ( i , i + 4)-stapling using copper catalysed azide alkyne cycloaddition. Linear and stapled peptidomimetics were analysed by circular dichroism (CD) and characterised in a membrane-based cAMP accumulation assay and in a bimane fluorescence assay on purified β 2 AR. Several peptidomimetics inhibited agonist isoproterenol (ISO) induced cAMP formation by lowering the ISO maximal efficacy up to 61%. Moreover, some peptidomimetics were found to significantly decrease the potency of ISO up to 39-fold. In the bimane fluorescence assay none of the tested peptidomimetics could stabilise an active-like conformation of β 2 AR. Overall, the obtained pharmacological data suggest that some of the peptidomimetics may be able to compete with the native G s protein for the intracellular binding site to block ISO-induced cAMP formation, but are unable to stabilise an active-like receptor conformation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

alpha-Diphenylphosphinoyl ketones are selectively and sequentially alkylated at the alpha-position. Double lithiation and selective alkylation occurs at the less stabilised gamma-position. Dephosphinoylation of the alkylation products gives ketones. Mono-alkylation is selective, highly crystalline intermediates are formed and a one-pot strategy is possible. The method is ideally suited for the preparation of acid-sensitive ketones.

The asymmetric synthesis of gamma-azido trans-cyclopropyl ketones is accomplished via a short, simple and efficient sequence. The cyclopropanation step is achieved by an intramolecular nucleophilic ring closure, with a diphenylphosphinate leaving group, to give trans-cyclopropane exclusively. beta-Keto-diphenylphosphine oxides cyclise to form optically active dihydrofurans. All possible diastereoisomers of dihydrofurans can be prepared selectively starting from the same olefin.

Treatment of 1,2-diols with diphenylphosphinoyl chloride in pyridine produces beta-chloroethyl phosphinates which react with complete control of stereochemistry to give epoxides and azido-alcohols, useful intermediates in cyclopropane synthesis.

The synthesis of enantiomerically-enriched trans-cyclopropane amino- and hydroxy-acids can be achieved by intramolecular ring closure in moderate to good yields. The optically active cyclopropane precursors are easily prepared in a short sequence from inexpensive, commercially available olefins and tert-butyl acetate. Several leaving groups and bases were compared for the cyclopropanation step, showing that the diphenylphosphinate and tosyl leaving groups give the best results when used in combination with either LDA or NaHMDS.

A silyloxy-THF has been converted into a cyclopropane containing three stereocentres as mixture of diastereoisomers. The mechanism of the reaction has been established and the source of stereochemical leakage proposed. An alternative stereospecific cascade reaction has been discovered.

Products of difficult ketone alkylation reactions can be made selectively via activation with a diphenylphosphinoyl group; subsequent dephosphinoylation is easily achieved in base.

Acyclic, achiral nucleoside derivatives 1b-e of adenine, cytosine, 5-methylcytosine, and guanine, containing a 3-hydroxy-2-(hydroxymethyl)prop-1-enyl group on N-1 or N-9, have been prepared analogously to the previously described thymine derivative 1a. In contrast to the adenine and guanine derivatives, the cytosine derivative 9 was unstable, and was obtained in a low yield due to side reactions. These include cleavage of the propenyl group from the base, and the formation of a bicyclic compound. The thymine derivative, although stable under neutral conditions, likewise underwent a reversible cyclization reaction (Michael addition) in the presence of acids or bases. The 5-methylcytosine derivative was stable under neutral and basic conditions. Four other nucleoside derivatives 26a-d containing a 2,3-dihydroxy-2-(hydroxymethyl)propyl group on N-1 or N-9, three of which are new, have likewise been prepared. All compounds were evaluated as antiviral agents against HIV-1 and HSV-1 but were devoid of antiviral activity.

In this paper we present revised and significantly improved synthetic routes to 2'-amino-LNA (locked nucleic acid). The optimal route is convergent with the synthesis of LNA monomers ("2'-oxy-LNA") via a common intermediate obtained by a mild deacetylation for the liberation of the 2'-hydroxy group to give compound 23 without the concomitant ring closure that affords the 2'-oxy-LNA skeleton. After inversion of the stereochemistry at C2' and triflate formation at the 2'-hydroxy group a new common intermediate 16 is obtained which gives easy access to a range of other analogues exemplified by the introduction of a sulfur nucleophile leading to the 2'-thio-LNA structure. After substitution of the triflate with azide a basic reduction affords the desired 2'-amino-LNA structure, i.e., compound 18. This new synthesis strategy towards 2'-amino-LNA improves the overall yield significantly and converges the syntheses of 2'-oxy-LNA and LNA analogues.