Synthesis of Cryptococcus neoformans Capsular Polysaccharide Structures. IV. Construction of Thioglycoside Donor Blocks and Their Subsequent Assembly

Di‐ and trisaccharide thioglycoside building blocks, ethyl (2,3,4‐tri‐O‐benzyl‐β‐d‐xylopyranosyl)‐(1→2)‐3‐O‐allyl‐4,6‐di‐O‐benzyl‐1‐thio‐α‐d‐mannopyranoside, ethyl (2,3,4‐tri‐O‐benzyl‐β‐d‐xylopyranosyl)‐(1→2)‐6‐O‐acetyl‐3‐O‐allyl‐4‐O‐benzyl‐1‐thio‐α‐d‐mannopyranoside and ethyl (2,3,4‐tri‐O‐benzyl‐β‐d‐xylopyranosyl)‐(1→4)‐[(2,3,4‐tri‐O‐benzyl‐β‐d‐xylopyranosyl)‐(1→2)]‐3‐O‐allyl‐6‐O‐benzyl‐1‐thio‐α‐d‐mannopyranoside, corresponding to repetitive structures in the capsular polysaccharide (CPS) of Cryptococcus neoformans have been synthesised using silver triflate‐promoted couplings between benzobromoxylose and properly protected mannose ethyl thioglycosides. The blocks contain an orthogonal allyl group in the 3‐position of the mannose residue to allow continued formation of the (1→3)‐linked mannan backbone of the CPS. They have benzyl ethers as persistent protecting groups to facilitate access to the acetylated target structures. Assembly of the blocks employing DMTST as promoter in diethyl ether afforded in high yield and complete stereoselectivity penta‐ and hexasaccharide motifs from C. neoformans serotype A–C. The latter were deallylated into new acceptors to allow synthesis of larger CPS‐fragments.     

Studies on Agarofurans IV. The Synthesis of 4-Substitutioned Agarofurans

A new synthetic route for α-agarofuran(1b) is described. Several agarofuran derivatives were synthesized in similar way. Derivative 1d was also synthesized in a novel way, in which the substitution at C-4 was performed quantitatively. An ideal condition for cyclization of diol 7 to agarofuran (1) was found.     

Studies on Agarofurans V. Studies on the Reductive Ring-Opening of 3,4-Epoxide of Agarofurans

The nature of reductive ring-opening of epoxide has been widely studied. But epoxides of agarofurans with rigid skeleton have their own specificity. Agarofurans have been found to be active on the nervous system in our institute. Reduction of epoxides may afford different types of agarofurans. This prompted us to investigate the reaction.Epoxides 1, 2, 3 were prepared by oxidation of their corresponding olefins1. Generally, the nature of the reduction of epoxides with LAH depends on the ster…     

Triterpene Glycosides of Astragalus and Their Genins. LXIV. Chemical Transformation of Cycloartanes. V. Synthesis of Cyclopycanthogenin from Cyclosiversigenin

The partial synthesis of cyclopycanthogenin, 20R,24S-epoxycycloartan-6,16,25-triol-3-one, was developed in four steps from cyclosiversigenin.     

Periphery-modified crown ethers. Synthesis of bis-5,8-dimethoxy-1,4-methanonaphthalene-fused crown ethers

The easily accessible and multi-functionalized 5,8-dimethoxy-6,7-dihydroxy methyl-1,4-dihydro-1,4-methanonaphthalene (1) has been utilized as the basic building material to synthesize the symmetric bis-methanonaphthalene-fused crown ethers 14a-d (BMN-16-crown-4, BMN-22-crown-6, BMN-28-crown-8, and BMN-34-crown-10), that are constructed based on the connection between the α,β-bis-benzylic carbon atoms of diol 1 and oligoethylene glycols (9a-d) via two synthetic routes keyed upon the method of Williamson ether synthesis.     

Pyrazolyl-benzoxazole derivatives as protein kinase inhibitors. Design and validation of a combinatorial library

The malfunctioning of protein kinases is a hallmark of numerous diseases, for which a satisfactory therapy is missing. We describe the design and synthesis of a kinase targeted library based on a novel 2-(3-phenyl-1H-pyrazol-4-yl)-1,3-benzoxazole scaffold. Ethyl 3-(3-nitrophenyl)pyrazole-4-carboxylate and its 4-nitro regioisomer were bound to trityl chloride resin, saponified with NaOH in MeOH, and amidated with a choice of two o-aminophenols. The resulting N-(2-hydroxyphenyl)amides were cyclized by Mitsunobu reaction to form four variants of the pyrazolyl-benzoxazole core template. Straightforward stannous chloride reduction of the nitro group on solid phase allowed subsequent scaffold derivatization via acylation or sulfonylation of the obtained amino function. Cleavage with TFA gave rise to the final compounds (36 examples).     

Synthetic Analogs of Natural Flavolignans. XIV. Synthesis and Transformations of 2' -Substituted Chalcones and Chalconepoxides

2' -Substituted chalcones and chalconepoxides have been synthesized. Their reactions with BF ³ etherate and hydrazine hydrate were studied     

Hetarylcyanamides. (Review)

The nomenclature and the synthesis of hetarylcyanamides and their reactions that take place at the cyanoamino group are discussed.