22 research outputs found
Skunk River Review January 1992, vol 3
https://openspace.dmacc.edu/skunkriver/1006/thumbnail.jp
Genome of the pitcher plant <i>Cephalotus </i>reveals genetic changes associated with carnivory
Carnivorous plants exploit animals as a nutritional source and have inspired long-standing questions about the origin and evolution of carnivory-related traits. To investigate the molecular bases of carnivory, we sequenced the genome of the heterophyllous pitcher plant Cephalotus follicularis, in which we succeeded in regulating the developmental switch between carnivorous and non-carnivorous leaves. Transcriptome comparison of the two leaf types and gene repertoire analysis identified genetic changes associated with prey attraction, capture, digestion and nutrient absorption. Analysis of digestive fluid proteins from C. follicularis and three other carnivorous plants with independent carnivorous origins revealed repeated co-options of stress-responsive protein lineages coupled with convergent amino acid substitutions to acquire digestive physiology. These results imply constraints on the available routes to evolve plant carnivory
Designing a Planar Chiral Rhodium Indenyl Catalyst for Regio- and Enantioselective Allylic C-H Amidation
© 2020 American Chemical Society Chiral variants of group IX Cp and Cp* catalysts are well established and catalyze a broad range of reactions with high levels of enantioselectivity. Enantiocontrol in these systems results from ligand design that focuses on appropriate steric blocking. Herein we report the development of a new planar chiral indenyl rhodium complex for enantioselective C-H functionalization catalysis. The ligand design is based on establishing electronic asymmetry in the catalyst, to control enantioselectivity during the reactions. The complex is easily synthesized from commercially available starting materials and is capable of catalyzing the asymmetric allylic C-H amidation of unactivated olefins, delivering a wide range of high-value enantioenriched allylic amide products in good yields with excellent regio- and enantioselectivity. Computational studies suggest that C-H cleavage is rate- and enantio-determining, while reductive C-N coupling from the Rh-v-nitrenoid intermediate is regio-determining11Nsciescopu
Development of Halomethyl-Triazole reagents for installation of protein post-translational modification mimics
Triazoles have been widely used as amide bond isosteres in chemical biology as linkers and
to enhance proteolytic stability. The use of triazoles has grown exponentially since the
discovery of the copper (I) catalysed alkyne azide cycloaddition reaction in 2002 as the
reaction is solvent and functional group tolerant, and usually high yielding. The reaction is
also orthogonal to reactions used in nature, meaning it has become a powerful coupling tool.
In post-translational modification (PTM), proteins are modified by covalent attachment of
functional groups to amino acid side chains. These PTM processes are generally thought to be
dynamic and highly regulated by cell machinery, controlling protein function in response to
stimuli. The ability to control function post protein synthesis allows organisms to have a
smaller genome, which is advantageous as it reduces the energy required for DNA replication
and repair. Research into the function of PTMs has been limited by the difficulty in generating
recombinant proteins that bear a single PTM in a specific location. Although many elegant
methods have been proposed that solve this problem, to date cysteine alkylation is one of the
most successful techniques. For lysine PTMs, thia-lysine II (sLys) derivatives have been
shown to be excellent mimics of lysine, where the only perturbation between the native lysine-containing
analogue is the switch of a CH2 for S in the side chain.
Biotin is a well-known PTM in biotin dependent carboxylases, where biotin is involved in CO2
transfer. Recently biotinylation has also been shown to be a PTM on many other proteins,
however the role of biotinylation is not well understood. Biotin triazole III has been shown to
be a good mimic of the biotin amide bond and retains excellent affinity to Avidin (Av). In
Chapter 1 the effects of modification to the valeryl side chain, and orientation of the biotin
triazole bond affect affinity to Av using ITC are investigated. Compounds III, V and VI are
shown to have a KD <120 pM, but further information on the binding affinity of these
compounds could not be assessed by ITC. Biotin triazoles III-VI were also shown to be
resistant to hydrolysis in serum, unlike the native biotin amide bond, which is hydrolysed by
the enzyme biotinidase (BTD). Generation of amide sLys derivatives has been shown to be synthetically challenging. In
Chapter 2, the synthesis and applications of chloromethyl-triazole biotin as a sulfhydryl
selective alkylation reagent are investigated. The electron withdrawing nature of the triazole
was proposed to give a ‘pseudo-benzylic’ halide α to the triazole, thus increasing reactivity.
The controlled alkylation of peptides and proteins has shown that chloromethyl-triazole biotin
shows enhanced reactivity over many commercial alkylation reagents and also gives good
selectivity for cysteine. Alkylation of histone H4K12C gave the singly alkylated product,
accompanied by low amounts of double alkylation. Biotinylation was confirmed by Western
blot with anti-biotin. Due to the wide range of readily available functional azides, it was envisaged that halomethyltriazoles
could be incorporated into other PTM mimics. In Chapter 3, efforts to expand the
range of PTMs accessible using halomethyl-triazoles and further enhance the reactivity of
chloromethyl triazoles by preparation of bromo- and iodomethyl triazoles are detailed.
Synthesis of reagents to mimic malonylation, succinylation and GlcNAcylation PTMs is
described and the reactivity of these halomethyl-triazole reagents is assessed. An alternate
approach to the development of PTM mimics through cysteine propargylation and subsequent
CuAAC coupling is also described in chapter 3.
In conclusion, a series of new reagents have been developed to mimic protein PTMs through
alkylation of cysteine. The reagents, which include biotin, GlcNAc, succinyl and malonyl
mimics, are based on a halomethyl-triazole scaffold and have been successfully reacted with
cysteine containing peptides and proteins