The triplex formation between the duplex and a single strand DNA has been shown to inhibit transcription at the specific DNA site, and expected as a new biological tool and a new therapeutic method in the so-called antigene strategy. However, native oligonucleotides can form triplexes only within the major groove of the homopurine-homopyrimidine stretch of DNA, and the triplex is destabilized either at a TA or a CG interrupting site. Despite a number of methods have been attempted to expand the limitation of triplex formation, this problem has not been generally solved. This review describes (1) molecular design to stabilize triplex at a TA or a CG interrupting site, including new recognition molecules which have been recently shown by the reviewer and coworkers to be specific toward each base pair. And (2) some method to enhance stability of triplexes with use of DNA binding molecules such as intercalators, cross-linking agents, and groove binders are also discussed.
Sequence-specific binding of small molecules to DNA is of considerable interest owing to its potential value in chemistry, biology, and medicine. Calicheamicin's oligosaccharide domain is endowed with striking DNA-binding properties targeting primarily 5'-TCCT-3' duplex DNA sequences. In this account, design and the total synthesis of two dimeric forms of the calicheamicin γ1Ioligosaccharide, the head-to-head dimer and the head-to-tail dimer are described. By using computer modeling, two dimers were designed to dock properly into the minor groove of duplex DNA along the sequences 5'- AGGA-XX-TCCT-3' and 5'-TCCT-TCCT-3', respectively. Syntheses of the dimers were completed by applying activated trichloroacetimidate of a fully protected oligosaccharide monomer. These designed dimers exhibited interesting DNA-binding properties and gene suppression activity.
Aromatic character of small-bridged cyclophanes of condensed benzenoid aromatics would be more sensitive to strain than that of the corresponding [n] paracyclophanes. In this context, we synthesized  (1, 4) anthracenophanes and  (9, 10) anthracenophanes, the smallest anthracenophanes thus far known, and investigated their structures and reactivities. Syntheses of these highly strained molecules were undertaken via two routes one; based on cleavage of the central bond of the [6.2.2] propellane skeleton and the other using benzoannelation to the  paracyclophane core. The parent 9, 10-bridged anthracene was fully characterized but it is too kinetically unstable for isolation, while the perisubstituted derivatives are stable owing to the steric protection. X-ray crystallographic structure analyses of the anthracenophanes revealed remarkable out-of-plane deformation of the bridged ring of the 9, 10-bridged anthracenes, but also notable bond length alternation in the 1, 4-bridged anthracene. 1H-NMR spectra indicate, however, that they retain aromaticity in spite of the severe distortion of the aromatic ring. Unusual reactivities were observed in particular in the electrophilic reactions of the 1, 4 -bridged anthracene such as acid-catalyzed telomerization, addition reactions to dienophiles presumably via zwitterion intermediates, and photochemical [2+2] dimerization. 9, 10-Bridged anthracenes underwent acid-catalyzed and photochemical isomerizations, giving methylenedihydroanthracenes and 9, 10-Dewar anthracenes, respectively.
The synthetic reaction using functionalized allylstannanes is widely appreciated as one of the most useful methods for the stereocontrolled C-C bond formation. We now report the stereoselective synthesis of functionalized heterocycles via the intramolecular reaction of allylstannane with aldehydes and imines. The stereocontrolled total synthesis of hemibrevetoxin B was achieved by using the intramolecular reaction of γ-alkoxyallylstannane with aldehydes. The extension of this methodology led to a new strategy for the stereoselective synthesis of alkaloids such as (+) -desoxoprosopinine and (+) -preussin.
The Mitsunobu reaction, a popular alkylation reaction utilizing the redox system between diethyl azodicarboxylate and triphenylphosphine, has a shortcoming that it can only be applied satisfactorily to a nucleophile (HA) of pKa less than 11. In order to overcome the limitation, we introduced several combinations of azodicarboxamides (TIPA, ADDP, TMAD, and DHTD) and tributylphosphine. In our continual search for new versatile reagents, we found cyanomethylenetrialkylphosphorane (CMBP, CMMP) was capable of mediating the alkylation of various HA of larger pKa than 11. Utilizing these reagents, the efficient alkylation of N-, C-, and O-nucleophiles, such as tosylamides, active methylene compounds, alcohols, and carboxylic acid was accomplished. The results are presented along with their synthetic application.
The application of enzymes or microorganisms to an organic synthesis is one of the most useful and practical methods for the preparation of optically active compounds. We have developed a novel process for enzymatic preparation of D- (-) -β-acetylthioisobutyric acid. A newly isolated strain, Pseudomonas putida MR-2068, produced an attractive esterase. A gene for the esterase was cloned and expressed in the Escherichia coli cells. The result of a sequence analysis and some characteristics of the purified enzyme are described. This esterase also catalyzed regio- and enantioselective hydrolysis of α-substituted carboxylic acid esters. Considering the results of enzymatic reactions, the active site model of enzyme is tentatively proposed.
It is believed that the aldose reductase (AR, EC 1.1.21), the initial enzyme of sorbitol pathway, plays a significant role in the initiation of diabetic complications. In a search for AR inhibitors, a series of 4-oxo-2-thioxothiazolidine-3-acetic acid derivatives was synthesized and showed the inhibitory activity against AR. (Z, E) -5- (2-Methyl-3-phenyl-2-propenylidene) -4-oxo-2-thioxothiazolidine-3-acetic acid (epalrestat) prevented the accumulation of sorbitol in rat sciatic nerve and rat blood cell, and improved motor nerve conduction velocity of diabetic rats. In clinical studies, epalrestat has shown the improvements in nerve function and subjective symptoms. In Japan, epalrestat was introduced on the market in January, 1992.