• Applied Chemistry for Engineering
• /
• v.9 no.6
• /
• pp.914-919
• /
• 1998

Optically pure $C_2-Symmetric$ pyrrolidine amides (8) were synthesized from readily available 1,2:5,6-di-O-isopropylidene-D-mannitol (1). Cyclization of dimesylated hexitol (4) with benzyl amine gave an inseparable mixture of $C_2-Symmetric$ pyrrolidine amine derivative (5) as a major product, concurring with its cis isomer (6) as a minor product. The pyrrolidine amines (5,6) were converted to separable pyrrolidine amides (8,9) via free amine (7). Optical purity of desired $C_2-Symmetric$ pyrrolidine amide (8a) was determined with its Mosher derivatives (13,14) by their $^1H$ and $^{19}F$ NMR spectra.

• Bulletin of the Korean Chemical Society
• /
• v.12 no.5
• /
• pp.565-569
• /
• 1991

Enantioselective synthesis of 1-substituted tetrahydroisoquinoline alkaloids (1) via asymmetric reduction of 1-substituted 3,4-dihydroisoquinolines (2) and the corresponding iminium salts (3) with the selected chiral hydride reagents, such as K glucoride (5), Itsuno's reagent (6), and Mosher's reagent (7) were examined. In these reactions, dihydroisoquinolines were not reduced by the hydride reagents, whereas the iminium salts were easily reduced under the same reaction conditions found in successful reduction of ketones. Thus, the reduction of 6,7-dimethoxy-3,4-dihydroisoquinolium iodide(3a) with 5, 6 and 7 provided the product 1a with 52.3 % ee, 18 % ee, and 66.4 % ee, respectively. For 1-benzyl derivatives (3b-3d), syntheses of 1b-1d with 0.7-6.2 % ee, 5.9-21 % ee, and 1.4-2.7 % ee were achieved with chiral reducing agents 5, 6 and 7, respectively. For 1-aryl derivatives, use of 5, 6 and 7 resulted in optical inductions in the range of 25.2-43 % ee, 13-21.1 % ee, and 6.3-16 % ee, respectively.

• YAKHAK HOEJI
• /
• v.43 no.5
• /
• pp.584-590
• /
• 1999

Bioactivity-directed fractionation from the seeds of Annona cherimolia resulted in the isolation of two known cytotoxic compounds : corrosolin (1) and compound-2 (2). The structures of these compounds were characterized on the basis of chemical and spectral data. Corrosolin has a relative stereochemical relationship of threo/trans/threo for the mono-tetrahydrofuran (THF) ring with two flanking hydroxyls, from C-15 to C-20, which is the annonacin type. Compound-2 has a relative stereochemical relationship of threo/trans/threo/trans/threo for the adjacent bis-THF ring with two flanking hydroxyls, such as in the asimicin type. The absolute configurations of carbinol carbons in corrosolin in corrosolin were determined as 10R, 15R, and 20R by analysis of its Mosher ester derivatives. Corrosolin and compound-2 are known, but are first isolated in this plant.

• Bulletin of the Korean Chemical Society
• /
• v.15 no.9
• /
• pp.732-739
• /
• 1994

Asymmetric [2,3]-Wittig rearrangements of allyl propargyl ethers in hexane were performed in the presence of s-butyllithium and (-)-${\alpha}$-isosparteine which is a $C_2$-symmetric chiral ligand for the alkyllithium reagent. The reactions of (Z)-or (E)-allyl 3-trimethylsilylpropargyl ethers at -78$^{\circ}C$ showed good diastereoselectivities (74-100%) and moderate enantioselectivities (29-71%). The absolute configurations of the rearrangement products were determined by the corresponding Mosher's esters. It was found that (-)-${\alpha}$ -isosparteine induced (R) configuration at the hydroxy carbon and syn stereochemistry more favorably. The possible transition state is discussed.

• Journal of Microbiology and Biotechnology
• /
• v.32 no.10
• /
• pp.1299-1306
• /
• 2022

Six ansamycin derivatives were isolated from the culture broth of Streptomyces sp. KCB17JA11, including four new hygrolansamycins A-D (1-4) and known congeners divergolide O (5) and hygrocin C (6). Compounds 1-5 featured an unusual six-membered O-heterocyclic moiety. The isolation workflow was guided by a Molecular Networking-based dereplication strategy. The structures of 1-4 were elucidated using NMR and HRESIMS experiments, and the absolute configuration was established by the Mosher's method. Compound 2 exhibited mild cytotoxicity against five cancer cell lines with IC₅₀ values ranging from 24.60 ± 3.37 µM to 49.93 ± 4.52 µM.