Chaofeng Dai

A Fluorescent Probe for Fast and Quantitative Detection of Hydrogen Sulfide in Blood

Hydrogen sulfide (H2S), well known for its unpleasant rotten egg smell, was traditionally considered as a toxic gas. However, recent studies have demonstrated that hydrogen sulfide is an endogenously produced gaseous signaling compound (gasotransmitter) with importance on par with that of the other two known endogenous gasotransmitters, nitric oxide (NO)[1] and carbon monoxide (CO).[2] H2S has been recognized for mediating a wide range of physiological effects. Studies have shown that H2S can have an effect on the cardiovascular system[3] by acting as a K-ATP channel opener.[4] Several studies have shown the protective roles of H2S, in situations such as myocardial ischemia, most likely through a combination of antioxidant and anti-apoptotic signaling.[5] Further studies also showed that H2S may be a therapeutic benefit for the treatment of ischemia-induced heart failure.[6-7] It is also a modulator in the central nervous system,[8-10] respiratory system, gastrointestinal system, and endocrine system.[11] It seems that hydrogen sulfide exhibits almost all the beneficial effects of NO without generating the toxic reactive oxygen species (ROS). In contrast, it also acts as an anti-oxidant or scavenger of ROS. Furthermore, research has indicated that hydrogen sulfide level is related to diseases such as Down syndrome[12] and Alzheimer’s disease.[13] Therefore, recent years have seen a steady increase in the interest in understanding hydrogen sulfide ’s physiological and pathological functions.[11, 14-15] One significant limiting factor in studying hydrogen sulfide is the lack of sensors and agents that allow for its rapid and accurate detection. There have been literature methods using colorimetric,[16-18] electrochemical analysis[19-21] and gas chromatography.[22-23] However, hydrogen sulfide catabolism is known to be fast, which could result in continuous fluctuation in its concentration, leading to difficulties in accurate analysis of this important molecule. Current methods do not allow for fast, accurate, and real-time determinations. Literature reported endogenous sulfide concentrations vary substantially among publications with most publications suggesting that sulfide concentration in blood is in the 10-100 μM range.[24-29] There are other studies suggesting sulfide concentration being much lower than this.[30-31] Therefore, there is an urgent need for the development of new methods for the efficient detection of sulfide in biological systems.

Using boronolectin in MALDI-MS imaging for the histological analysis of cancer tissue expressing the sialyl Lewis X antigen

Certain carbohydrate-based biomarkers are known to correlate with cancer formation and progression. By targeting sialyl Lewis X, we have developed the first boronolectin-MS tag conjugate, which allows for MALDI-based imaging of cancer based on its cell surface carbohydrate.

Click reactions and boronic acids: applications, issues, and potential solutions.

Boronic acids have been widely used in a wide range of organic reactions, in the preparation of sensors for carbohydrates, and as potential pharmaceutical agents. With the growing importance of click reactions, inevitably they are also applied to the synthesis of compounds containing the boronic acid moiety. However, such applications have unique problems. Chief among them is the issue of copper-mediated boronic acid degradation in copper-assisted [2,3]-cycloadditions involving an alkyne and an azido compound as the starting materials. This review summarizes recent developments, analyzes potential issues, and discusses known as well as possible solutions.

Boronic acid-modified DNA that changes fluorescent properties upon carbohydrate binding

A long wavelength boronic acid-modified TTP (NB-TTP) has been synthesized and enzymatically incorporated into DNA. Such DNA shows intrinsic fluorescent changes upon carbohydrate addition.

3,6-Substituted-1,2,4,5-tetrazines: tuning reaction rates for staged labeling applications

Cycloaddition reactions involving tetrazines have proven to be powerful bioorthogonal tools for various applications. Conceivably, sequential and selective labeling using tetrazine-based reactions can be achieved by tuning the reaction rate. By varying the substituents on tetrazines, cycloaddition rate variations of over 200 fold have been achieved with the same dienophile. Upon coupling with different dienophiles, such as norbornene, the reaction rate difference can be over 14,000 fold. These substituted tetrazines can be very useful for selective labeling under different conditions.

2,6-Dansyl Azide as a Fluorescent Probe for Hydrogen Sulfide

A second-generation sulfonyl azide-based fluorescent probe, 2,6-DNS-Az, has been developed for the quantitative detection of H2S in aqueous media such as phosphate buffer and bovine serum. Compare to the first-generation 1,5-DNS-Az probe, this probe shows both high sensitivity in phosphate buffer without the need for addition of surfactant and selectivity for sulfide over other anions and biomolecules, and thus can be used as a useful tool for detection of H2S in the biological system.

Rapid and Specific Post‐Synthesis Modification of DNA through a Biocompatible Condensation of 1,2‐Aminothiols with 2‐Cyanobenzothiazole

Post-synthesis modification of DNA is an important way of functionalizing DNA molecules. Herein, we describe a method that first enzymatically incorporates a cyanobenzothiazole (CBT)-modified thymidine. The side-chain handle CBT can undergo a rapid and site-specific cyclization reaction with 1,2-aminothiols to afford DNA functionalization in aqueous solution. Another key advantage of this method is the formation of a single stereo/regioisomer in the process, which allows for precise control of DNA modification to yield a single component for aptamer selection work and other applications.

Carbohydrate biomarker recognition using synthetic lectin mimics

Carbohydrate biomarkers play very important roles in a wide range of biological and pathological processes. Compounds that can specifically recognize a carbohydrate biomarker are useful for targeted delivery of imaging agents and for development of new diagnostics. Furthermore, such compounds could also be candidates for the development of therapeutic agents. A tremendous amount of active work on synthetic lectin mimics has been reported in recent years. Amongst all the synthetic lectins, boronic-acid-based lectins (boronolectins) have shown great promise. Along this line, four classes of boronolectins including peptide-, nucleic-acid-, polymer-, and small-molecule-based ones are discussed with a focus on the design principles and recent advances. We hope that by presenting the potentials of this field, this review will stimulate more research in this area.

Design, Synthesis, and Polymerase‐Catalyzed Incorporation of Click‐Modified Boronic Acid–TTP Analogues

DNA molecules are known to be important materials in sensing, aptamer selection, nanocomputing, and construction of unique architectures. The incorporation of modified nucleobases affords unique DNA properties for applications in areas that would otherwise be difficult or not possible. Earlier, we demonstrated that the boronic acid moiety can be introduced into DNA through polymerase-catalyzed reactions. In order to study whether such incorporation by polymerase is a general phenomenon, we designed and synthesized four boronic acid-modified thymidine triphosphate (TTP) analogues. The synthesis of certain analogues was through the use of a single dialkyne tether for both the Sonogashira coupling with thymidine and the later Cu-mediated [3+2] cycloaddition for linking the boronic acid moiety. This approach is much more efficient than the previously described method, and paves the way for the preparation of a large number of boronic acid-modified TTPs with a diverse set of structural features. All analogues showed very good stability under polymerase chain reaction (PCR) conditions and were recognized as a substrate by DNA polymerase, and thus incorporated into DNA.

The first chemical synthesis of boronic acid-modified DNA through a copper-free click reaction

The first chemical incorporation of the boronic acid group into DNA using a copper-free click reagent was reported. Compared with the PCR-based method, this approach allows for site-specific incorporation and synthesis on a larger scale.