Mikołaj Chromiński

Reduction-free synthesis of stable acetylide cobalamins

A straightforward, reduction-free method for the synthesis of organometallic cobalamins has been developed. Stable phenylacetylide derivatives were characterized by X-ray analysis, showing a pronounced influence of the electronic nature of substituents on their structure.

Prolinethioamides versus Prolinamides in Organocatalyzed Aldol Reactions—A Comparative Study

Various organocatalysts have been developed for the aldol reaction but particular attention has been paid to prolinamide derivatives. They are easy to prepare and their catalytic activity can be readily tuned through structural modification. In this review, the comparison of catalytic activities between prolinethioamides and their respective amides in direct asymmetric aldol reactions is presented.

Porphyrins as substrates in CuAAC — exclusion of unwanted copper insertion into the macrocyclic core

Unwanted copper insertion into a free base porphyrin starting material during Cu-catalyzed [1,3] azide-alkyne dipolar cycloaddition (CuAAC) is not observed when using (1,10-phenanthroline)-bis(triphenylphosphine)copper(I) nitrate as a catalyst. Reactions give 1,4-disubstituted 1,2,3-triazoles in good yields for a broad range of porphyrins. 1,5-Disubstituted 1,2,3-triazole cycloadducts can be generated in the presence of Cp*RuCl(COD).

Synthesis and Evaluation of Bifunctional sGC Regulators: Optimization of a Connecting Linker

Hybrid molecules composed of PpIX and cobyrinic acid derivatives conjugated through linkers of varying length and composition were prepared via 1,3-dipolar cycloaddition (CuAAC) or amidation/esteryfication reactions. They were tested for activation of soluble guanylyl cyclase (sGC), a key enzyme in the NO/cGMP signaling pathway, by an in vitro GTP→cGMP conversion assay. Using purified heme-deficient sGC and truncated sGC variants lacking a heme-binding domain, we demonstrated that such hybrid molecules may activate sGC by targeting heme-binding and/or catalytic domain. While all conjugates activated sGC, only selected compounds served as bifunctional regulators and were capable of simultaneous targeting both heme and catalytic domains of sGC. The length and type of a linker connecting both components had a profound effect on the extent of sGC activation, indicating that the linkers type is crucial for their binding affinities with regulatory and catalytic domains. Only hybrids with the conjugated linker of 13-16 atom length synergistically target both domains and displayed the lowest EC50 and highest activating potency. Compounds with shorter connecting linkers were much less potent and were no more active than the cobyrinic acid component alone. The most active conjugate, which showed a 60-fold activation of sGC, was compound 11, in which PpIX and cobyrinic acid components are separated by 11 atoms chain with the triazole moiety in between.

Selective modifications of hydrophobic vitamin B12 derivatives at c-and d-positions.

The acid-sensitivity of vitamin B(12) derived mono- and diamides was studied. It was found that the use of reductive ring-opening of the lactone moiety deactivated undesired decomposition of c-mono- and c,d-diamides under acidic conditions. As a result, reactions gave respectively c- or d-acids which were further functionalized via coupling with amino acids. Though mono- and diamides exhibited acid sensitivity, they were used for the preparation of several highly functionalized molecules showing their stability under various reaction conditions.

A multicolor riboswitch-based platform for imaging of RNA in live mammalian cells

RNAs directly regulate a vast array of cellular processes, emphasizing the need for robust approaches to fluorescently label and track RNAs in living cells. Here, we develop an RNA imaging platform using the cobalamin riboswitch as an RNA tag and a series of probes containing cobalamin as a fluorescence quencher. This highly modular ‘Riboglow’ platform leverages different colored fluorescent dyes, linkers and riboswitch RNA tags to elicit fluorescence turn-on upon binding RNA. We demonstrate the ability of two different Riboglow probes to track mRNA and small noncoding RNA in live mammalian cells. A side-by-side comparison revealed that Riboglow outperformed the dye-binding aptamer Broccoli and performed on par with the gold standard RNA imaging system, the MS2-fluorescent protein system, while featuring a much smaller RNA tag. Together, the versatility of the Riboglow platform and ability to track diverse RNAs suggest broad applicability for a variety of imaging approaches.A new riboswitch-based RNA sensor called Riboglow binds to quenched fluorescent probes to induce fluorescence turn-on. Riboglow enables tagging and tracking of mRNA and short noncoding RNAs with different colored fluorophores in live mammalian cells.

Vitamin B12 Phosphate Conjugation and Its Effect on Binding to the Human B12 -Binding Proteins Intrinsic Factor and Haptocorrin.

The binding of vitamin B12 derivatives to human B12 transporter proteins is strongly influenced by the type and site of modification of the cobalamin original structure. We have prepared the first cobalamin derivative modified at the phosphate moiety. The reaction conditions were fully optimized and its limitations examined. The resulting derivatives, particularly those bearing terminal alkyne and azide groups, were isolated and used in copper-catalyzed alkyne-azide cycloaddition reactions (CuAAC). Their sensitivity towards light revealed their potential as photocleavable molecules. The binding abilities of selected derivatives were examined and compared with cyanocobalamin. The interaction of the alkylated derivatives with haptocorrin was less affected than the interaction with intrinsic factor. Furthermore, the configuration of the phosphate moiety was irrelevant to the binding process.

Development of a riboswitch-based platform for live cell imaging of RNAs in mammalian cells

RNAs directly regulate a vast array of cellular processes, emphasizing the need for robust approaches to fluorescently tag and track RNAs in living cells. Here, we develop an RNA imaging platform using the Cobalamin (Cbl) riboswitch as an RNA aptamer and a series of probes containing Cbl as a fluorescent quencher linked to a range of fluorophores. We demonstrate fluorescence turn-on upon RNA binding and proof of concept for tracking both mRNA and small U RNA in live cells.RNAs directly regulate a vast array of critical cellular processes, emphasizing the need for robust approaches to fluorescently tag and track RNAs in living cells. Here, we develop an RNA imaging platform using the cobalamin riboswitch as an RNA tag and a series of probes containing cobalamin as a fluorescence quencher. This highly modular ‘Riboglow’ platform leverages different color fluorescent dyes, linkers and riboswitch RNA tags to elicit fluorescent turn-on upon binding RNA. We demonstrate the ability of two different Riboglow probes to track mRNA and small non-coding U RNA in live mammalian cells. A direct side-by-side comparison revealed that Riboglow outperformed the dye binding aptamer Broccoli and performed on par with the current gold standard RNA imaging system, the MS2-fluorescent protein system, while featuring a much smaller RNA tag. Together, the versatility of the Riboglow platform and ability to track diverse RNAs suggest broad applicability for a variety of imaging approaches. Graphical abstract

Synthesis and evaluation of bifunctional sGC regulators

Background Our previous studies identified dicyanocobinamide as a novel sGC regulator that targets the catalytic region and synergistically enhances activation of sGC by NO-independent regulators. As proof-of-concept study, we designed and synthesized a set of bifunctional sGC regulators, which consist of cobinamide analog conjugated to a protoporphyrin IX derivative through linkers of varying length and composition (Figure 1). Results The length and composition of the linker was proved to be crucial for sGC activation. Our results indicate that only hybrid molecules containing a 13-16 atom chain linker benefited from synergistic engagement of both heme-binding region and catalytic domain. The hybrid compounds containing linkers connected through an ester bond were not only more stable, but also were more effective than those connected though an amide. Hybrids with shorter or longer linkers, or with different linker composition, were much less potent and were no more active than the cobyrinic acid component alone. The most effective compound was conjugated through an ester bond, contained a 13 atom chain linker and a triazole group close to the cobyrinate moiety. This compound displayed more than 60 fold activation of purified sGC.