Organizing Committee

Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

One of the programs in our laboratory deals with modification of sucrose molecule at the terminal positions. As a part of this program several macrocyclic receptors containing sucrose unit were prepared.^1-3 Due to poor properties of such compounds in molecular recognition⁴ we have focused our attention on preparing such derivatives possessing C₂ symmetry. Key-compound - 6’-O-tert-butyl-diphenylsilyl-1’,2, 3,’3’,4,4’-hexa-O-benzylsucrose (2), obtained from the known diol (1)^1,3 in 60% yield, was converted into 6’-O-acroyl-6-O-allyl- (3) or 6 [(2-p-toluenesulfonyloxy)ethyl]- (4) derivatives. Reaction of 3 under RCM conditions gave a mixture of products, from which the C₂ symmetrical compound 5 was isolated by HPLC as well as both internal ring-closing and one linear dimeric products. Treatment of (4) with sodium hydride in DMF surprisingly² afforded mostly cyclization product 6, however small amounts of the expected compound 7 were also isolated.

1. 
   M. Mach, S. Jarosz, A. Listkowski, J. Carbohydr. Chem., 2001 (20) 485-493;
   
2. 
   S. Jarosz, A. Listkowski, M. Mach, Polish J. Chem., 2001 (75) 638-687;
   
3. 
   S. Jarosz, A. Listkowski, J. Carbohydr. Chem., 2003 (22) 753-763;
   
4. 
   S. Jarosz, A. Listkowski, B. Lewandowski, Z. Ciunik, A. Brzuszkiewicz, Tetrahedron, 2005, accepted.
   

THE LIAISON BETWEEN HYPERVALENT IODINE REAGENTS AND CARBOHYDRATE CHEMISTRY

Andreas KIRSCHNING

Institute of Organic Chemistry, Universiy of Hannover, Schneiderberg 1B, 30167 Hannover, Germany

Hypervalent (III) reagents are known since 1886 when Willgerodt described dichloro iodosobenzene for the first time. Only during the past two decades hypervalent iodine reagents in the oxidation states +1 to +5 have seen a broad interest among synthetic organic chemists.¹ Besides the Dess-Martin periodinane, IBX has recently appeared as a versatile oxidation agent on the laboratory shelves. Hypervalent iodine reagents in the oxidation state +3 show resemblance to organometallic reagents as they undergo ligand exchange reactions as well as reductive eliminations. Particularly the latter property allows to perform unique oxidations which rarely has been exploited in natural product synthesis including carbohydrate chemistry.

Over the past decade we have developed several synthetic applications for saccharides using iodine(III) reagents. The report will focus on these new synthetic applications.² These will include oxidations, glycosidations and other transformations. In addition, mechanistic studies and applications in solid-phase assisted synthesis will be addressed.

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¹ A. Varvoglis, Hypervalent Iodine in Organic Synthesis, Academic Press, San Diego 1997

M. Ochiai, Top. Curr. Chem. 2003, 224, 5-68.

² A. Kirschning, Eur. J. Org. Chem. 1998, 2276-2274.

BIODIVERSITY EXPLOITATION FOR THE SEARCH OF BIOACTIVE SUGARS

Amélia Pilar RAUTER
Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Edifício C8, 5º Piso, 1749-016 Lisboa, Portugal.

E-mail: [e-mail]; Tel: [phone]; Fax: [phone]

Bioactive natural products present a wide variety of chemical structures, being some structural units responsible for a great diversity of bioactivities, namely lactones, heterocyclic rings and flavonoid moieties. In this work we will report on the development of synthetic strategies leading to sugar derivatives which contain those bioactive units, among others. The evaluation of their biological activities will also be presented and the results obtained will be discussed and correlated to their structure and stereochemistry.

Chain elongation, followed by the construction of lactones or heterocyclic moieties linked to position 4 of the furanose ring, gave compounds exhibiting neuroactivity in insects, presenting some of them a remarkable insecticidal activity against flies. One of the pseudo-C-nucleosides inhibited butyrylcholinesterase, an enzyme involved in neurotransmission in the brain. Its inhibition has been found to exert a beneficial therapeutic effect in some patients suffering from Alzheimer’s disease.
Efficient and direct approaches to macrocyclic bislactones or five-membered ring lactones linked/fused to furanose/pyranoside moieties will be described and discussed their structure/fungicidal efficacy relationship.
Trichloroacetimidates and glycals were the glycosyl donors investigated for the preparation of flavonoid O-glycosides. Among them, the synthesis of anthocyanidin glycosides starting from trichloroacetimidates was particularly challenging, considering the properties of these pigments related to their solubility and instability. The experimental procedure was easy to carry out, leading to the stereoselective synthesis of the target molecules in moderate yield. Glycals led to the stereoselective synthesis of 2-deoxy-O-glycosides -anomer or to the corresponding Ferrier products, when promoted by triphenylphosphine hydrobromide or acid zeolite, respectively. These reactions were extended to other acceptor molecules such as sterols, sugars, thiols and heterocyclic bases. When aliphatic alcohols were the glycosyl acceptors, some of the 2-O-glycosides obtained exhibited surface active and antibacterial properties, being one of them selective over Bacillus species including Bacillus cereus, a human pathogen bacteria close related to Bacillus anthracis.


RHODIUM-CATALYZED INTRAMOLECULAR CONJUGATE ADDITION OF VINYLSTANNANES TO 2,3-DIHYDRO-4-PYRIDONES. AN EFFICIENT ROUTE TO STEREOSELECTIVE CONSTRUCTION OF AZABICYCLIC RING SYSTEMS.