An efficient synthesis of 4-ethyl-4-[(3-hydroxycarbonyl)propyl]dihydro-2(3H)-furanone and its use in a formal total synthesis of (±)-quebrachamine

An organocatalytic Michael-cyclization cascade of 4-oxa-α,β-unsaturated carboxylic acids with aldehydes: facile synthesis of chiral γ-lactols and trisubstituted γ-lactones

An organocatalytic Michael-cyclization cascade of 4-oxa-α,β-unsaturated carboxylic acids with aldehydes has been developed, enabling highly enantioselective synthesis of γ-lactols, trisubstituted γ-lactones and γ-lactams.

A Review on Recent Developments in Syntheses of the post-Secodine Indole Alkaloids. Part II: Modified Alkaloid Types

The second part of the planned review on developments in the field of total and formal total synthesis of the post-secodine indole alkaloids concentrates on modified alkaloid types, i.e. those skeletons derived from primary types by formation of additional and/or rupture of existing bonds, while connectivities next to indol(e)ine moiety remain intact. It thus reviews the synthesis of alkaloids of quebrachamine/cleavamine type including VLB-bis-indoles, rhazinilam type, aspidofractinine/kopsane and kopsifoline type, as well as kopsijasminilam alkaloids, lapidilectine B and danuphylline. It covers the literature of from 1991-1992 up to approximately end 2006. A review with 174 references.

Highly Stereoselective β-Anomeric Glycosidation of a 2‘-Deoxy Syn-5‘-Configured 4‘-Spironucleoside

A direct enantioselective pathway that delivers exclusively the beta-anomer of a 4'-spironucleoside has been successfully developed. The key starting material is the enantiomerically pure dihydroxy lactone 19, which has proven amenable to conversion to glycal 22 via the chloro acetonide. This intermediate is then capped as the 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) glycal. The latter can enter into N-iodosuccinimide-promoted glycosidation with persilylated thymine. Only the beta anomer is formed. Ensuing deiodination and desilylation proceed quantitatively to furnish the targeted, previously elusive anomer.

Asymmetric synthesis of (-)-eburnamonine and (+)-epi-eburnamonine from (4S)-4-ethyl-4-[2-(hydroxycarbonyl)ethyl]-2-butyrolactone

The key chiral nonracemic 4,4-disubstituted 2-butyrolactone carboxylic acid, (S)-4, is readily accessible via an efficient and stereospecific dirhodium(II) tetraacetate catalyzed tertiary C-H insertion reaction of the diazomalonate (S)-5. The coupling of the acid (S)-4 with tryptamine produces the amide (S)-3, which is then transformed into the aldehyde 23 and hydroxy-lactam 24. Acid-mediated Pictet-Spengler cyclization of 23 and 24 produces the tetracyclic indole lactams (1S,12bS)-25a and (1S,12bR)-25b. Compounds 25a and 25b are converted, via the lactam alcohols 30a and 30b, to (-)-eburnamonine (1a) and (+)-epi-eburnamonine (1b).

Synthesis of novel 3'-C-methyl-apionucleosides: an asymmetric construction of a quaternary carbon by Claisen rearrangement

The synthesis of 2,3-dideoxy-3-C-(hydroxymethyl)-3-C-methyl-D-glycero-tetrofuranosyl++ + nucleosides was accomplished in high enatiomeric purity (98.5% ee) via [3,3]-sigmatropic Claisen rearrangement of (E)(S)-5-benzyloxy-1-tert-butyldimethylsilanyloxy-4-methyl-pent-3- en-2-ol prepared from 2,3-O-isopropylidene-D-glyceraldehyde. The synthesized nucleosides were assayed against human immunodeficiency virus (HIV) and hepatitis B virus in human peripheral blood mononuclear (PBM) and 2.2.15 cells, respectively. 6-Amino-9-[2,3-dideoxy-3-C-(hydroxymethyl)-3-C-methyl-beta-D-glycero- tetrofuranosyl]-2-fluoropurine shows moderate antiviral activity (EC50 = 2.55 microM) against HIV-1 strains and 6-amino-9-[3-deoxy-3-C-(hydroxymethyl)-3-methyl-alpha-D-glycero-tetro furanosyl]-2-fluoropurine exhibits potent anti-HIV activity (EC50 = 0.073 microM) with significant cytotoxicity (IC50 = 1.0 microM).