The synthetic method of optically active compound by using lipase-catalysis in organic solvent has been generally accepted recently. Because lipases possess especially broad substrate specificity and are commercially available. However, efficient substrates of lipase-catalyzed asymmetric reactions were limited to be the compounds whose stereogenic carbon atoms were in the neighborhood of the reaction site.
This review describes our investigation on substrates of which stereogenic carbon atoms are remote from the reacting site, leading to lipase-catalyzed asymmetric synthesis of optically active synthetic drugs.

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Controlling of the π-facial stereoselectivity in Diels-Alder reactions has been one of the most fundamental and attractive subjects of theoretical and experimental studies.
Increasing attention has been focused on the selectivity in the reaction of 5-substituted cyclopentadienes, the simplest diene having unsymmetrical π-plane. The, π-facial selectivity is highly dependent on the substituents 1) The diene having 5-alkyl or 5-trimethylsilyl group reacted with dienophiles with anti-π-facial selectivity; 2) 5-Hydroxy, 5-acetoxy, or 5-fluoro moiety leads to the opposite stereochemical results. The former case is simply attributable to the steric repulsion between the substituents and dienophiles. However, the origin of the syn selectivity in the latter case has been the subject of intensive studies.
The present paper describes a short review on the theories developed for the prediction and explanation of the π-facial selectivity in the Diels-Alder reactions of these simple dienes.

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Photochemical reactions of thioamides and thioimides are reviewed. Topics included are (1) photochemical [2+2] cycloaddition reactions of thioamides and thioimides with alkenes, (2) photochemical hydrogen abstraction of thioamides and thioimides by the thiocarbonyl sulfur atom.

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Design and synthesis of artificial systems for regulation of ion recognition utilizing external information at molecular level, i.e. metal ion, electron, organic molecule, are described. Pseudocrowns formed by coordination of heavy metal ion as an effector are useful frameworks for controlling recognition of metal ions and provide an interesting feature for construction of a chiral host because of their molecular chirality. Structural change of recognition site induced by redox reactions between thiol and disulfide is also a very effective way of regulating ion recognition. In particular, a new concept of redox gate affords one of the most ideal systems for perfect switching (quantitative interconversion, completely different ion affinity between the two redox forms, stability toward autoxidation) of Ag⁺ recognition. A system controlling metal binding is also described which is constructed by molecular assembling via triple hydrogen bonding between a receptor and guests containing a short polyether chain.

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Dimethylformamide-sulfur trioxide (DMF-SO₃) complex was found to be more suitable for tyrosine sulfation than pyridine-sulfur trioxide (pyridine-SO₃) complex, the most commonly used sulfur trioxide complex for sulfation. In addition, a new method for the effective reduction of methionine sulfoxide [Met(O)] in protected peptides was established using DMF-SO₃ complex in the presence of nucleophile such as thiol or iodide ion. Based on these findings concerning DMF-SO₃ complex, a unique synthetic method for tyrosine-sulfate [Tyr(SO₃H)] containing peptide was developed. In this methodology, the p-(methylsulfinyl) benzyl : (Msib) group, a safety-catch type protecting group, was used as a key protecting group for the alcoholic hydroxyl function of Ser/Thr in order to achieve the selective sulfation on Tyr. An effective acidic deprotection system to minimize the decomposition of sulfate ester on Tyr(SO₃H) residue was also developed. Several biologically active Tyr(SO₃H) -containing peptides were prepared by this new method.

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Recently, “difficult sequences” have been often found as a key word in solid-phase peptide synthesis. “Difficult sequences” which cause the most serious potential problem during stepwise solid-phase peptide synthesis result from the intermolecular aggregation, namely, the formation of β-sheet structure by intermolecular hydrogen bonds between protected peptide chains. This β-sheet structure hinders the coupling reaction, the deprotection of the N-protecting group, and even the liberation of amino groups at each step for peptide chain elongation and results in the incomplete peptides with the properties similar to the target peptide. In liquid phase peptide synthesis, the “difficult sequence” is closely related to the solubility of protected peptides. The decreasing solubility of protected peptides in organic solvents along with increasing their chain length is due to the intermolecular β-sheet structure formation. The conversion of “difficult sequence” to easy sequence by disrupting the β-sheet structure can be achieved wherether the protected peptides are completely solvated by organic solvents or they are subject to peptide segment separation.

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