Highly Precise Protein Semisynthesis through Ligation-Desulfurization Chemistry in Combination with Phenacyl Protection of Native Cysteines.

Semisynthesis of proteins via expressed protein ligation is a powerful tool to furnish full-length proteins carrying site-specific (posttranslational) modifications. The development of various β-mercapto amino acid building blocks coupled with ligation-desulfurization chemistry enabled further advances in this methodology by alleviating the need for cysteine residues at the desired ligation sites. However, this expansion in the availability of viable ligation sites is sometimes counterbalanced by the inadvertent desulfurization of unprotected native cysteines, which might be of structural and/or functional importance.

Utility of the Phenacyl Protecting Group in Traceless Protein Semisynthesis through Ligation-Desulfurization Chemistry.

Semisynthesis of proteins via expressed protein ligation is a widely applicable method, even more so because of the possibility of ligation at non-cysteine sites using β-mercapto amino acids that can be converted to the corresponding native amino acids by desulfurization. A drawback of this ligation- desulfurization approach is the removal of any unprotected native cysteine residues within the ligated protein segments. Here, we show that the phenacyl (PAc) moiety can be successfully used to protect cysteines within recombinantly generated protein segments.

Impaired Chaperone Activity of Human Heat Shock Protein Hsp27 Site-Specifically Modified with Argpyrimidine.

Non-enzymatic posttranslational modifications (nPTMs) affect at least ∼30 % of human proteins, but our understanding of their impact on protein structure and function is limited. Studies of nPTMs are difficult because many modifications are not included in common chemical libraries or protein expression systems and should be introduced site-specifically. Herein, we probed the effect of the nPTM argpyrimidine on the structure and function of human protein Hsp27, which acquires argpyrimidine at residue 188 in vivo.

Arginine side-chain modification that occurs during copper-catalysed azide-alkyne click reactions resembles an advanced glycation end product.

Dehydroascorbate is a by-product of copper-catalysed azide-alkyne click (CuAAC) reactions and also forms advanced glycation end products (AGEs) in tissues undergoing oxidative stress. Here we isolate and characterize an arginine-dehydroascorbate adduct formed during CuAAC reactions, investigate strategies for preventing its formation, and propose its biological relevance as an AGE.

A total synthesis prompts the structure revision of haouamine B.

A concise asymmetric approach to the indeno-tetrahydropyridine core of the unusual alkaloid haouamine B allowed for an investigation of a biomimetic oxidative phenol coupling as a proposed biosynthetic step, and ultimately provided access to the published structure of the natural product. As a consequence of our synthetic studies, the structure of haouamine B has been revised.

Biological evaluation of ent-narciclasine, ent-lycoricidine, and certain enantiomerically-related congeners.

The non-natural enantiomeric forms of narciclasine and lycoricidine ((-)-1 and (-)-2, respectively), as well as congeners 3-6 are available through chemoenzymatic synthesis. Accordingly, they have now been tested for their cytotoxic effects in a 13-member human cancer cell-line panel and found to be only weakly active. In contrast, an authentic sample of the natural enantiomeric form of narciclasine ((+)-1) was found to be highly active in the same screens.

A chemoenzymatic total synthesis of the structure assigned to the alkaloid (+)-montabuphine.

An enantioselective synthesis of the structure, 3, assigned to the alkaloid (+)-montabuphine has been achieved using the readily available metabolite 4 as starting material. A comparison of the physical and spectral data recorded on compound 3 with those reported for (+)-montabuphine suggests that they are different compounds.

Chemoenzymatic approaches to lycorine-type Amaryllidaceae alkaloids: total syntheses of ent-lycoricidine, 3-epi-ent-lycoricidine, and 4-deoxy-3-epi-ent-lycoricidine.

The readily available and enzymatically derived cis-1,2-dihydrocatechol 4 has been elaborated, over 11 steps including an Overman rearrangement, into the non-natural enantiomer, (-)-1, of the alkaloid lycoricidine [(+)-1]. Related chemistries have provided analogues 18, 19, and 26.