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.     

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     

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).     

Preparation of chiral 4-substituted γ-lactams and the corresponding γ-aminobutyric acids. (Review)

Data on the synthesis of chiral γ-lactams substituted at position 4 and the corresponding β-substituted γ-aminobutyric acids for the period from 1991 to 2006 are reviewed. Dedicated to Prof. Ivars Kalvinsh to mark his 60^th birthday __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 803–816, June, 2007.     

Neoflavones. 2. Methods for Synthesizing and Modifying 4-Arylcoumarins

Literature data up to 2003 were presented and information on methods for preparing and modifying natural 4-arylcoumarins and their synthetic analogs were systematized.__________Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 199–218, May–June, 2005.     

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.     

Synthesis of polyamines and polyamine toxins. An improved alkylation procedure

Polyamines and polyamine toxins are biologically important molecules, having modulatory effects on nucleotides and proteins. Here we present an improved alkylation procedure, which allows sequential synthesis of polyamines and polyamine toxins on solid phase using N-protected aminoalkyl halides and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) as base. The feasibility of the procedure is demonstrated with the synthesis of the native polyamine toxin, PhTX-433, as well as an analogue, PhTX-56, which is a very potent and subtype selective glutamate receptor antagonist.