Current Organic Chemistry, Volume 6, No. 5, 2002
Current Synthetic Approaches to Peptide and Peptidomimetic Cyclization Pp.411-440
Peng
Li, Peter P. Roller and Jiecheng Xu
Right or Left – Enantioselective Catalysis.
New Ni, Pd and Pt Phosphane Complexes with the Chiral 9‑Phenyldeltacyclanyl
Substituent Pp.441-451
Henri
Brunner
Biocatalysis Applied to the Synthesis of Vitamin D Analogues Pp.453-469
Susana
Fernández, Vicente Gotor-Fernández, Miguel Ferrero,and Vicente Gotor
The Synthesis of Disaccharides, Oligosaccharides and Containing Thiosugars Pp.471-491
Inmaculada
Robina and Pierre Vogel
Abstracts
[Back to top] Current Synthetic Approaches to Peptide and Peptidomimetic Cyclization
Peng Li, Peter P. Roller and Jiecheng Xu
An increasingly
large number of bioactive cyclic peptides have been found in nature. The
enhanced biological specificity, activity, and metabolic stability of
cyclopeptides, by virtue of their conformationally constrained structural
feature, have attracted much attention and made these compounds extensively
studied. Cyclic peptidomimetic scaffolds and templates have been widely used to
assemble various spatially defined functional groups for molecular recognition
and drug discovery. These efforts are complemented optimally by NMR and X-ray
based structure information, and assisted by molecular modeling based structure
predictive methods. Peptide cyclization also becomes an effective and commonly
employed strategy for peptide modifications. During the past several decades,
great effort has been made to develop more efficient methods for the synthesis
of cyclic peptides and peptidomimetics, as potential drug leads and/or as
models for conformational analysis. This review is aimed at highlighting novel
recently developed peptide cyclization approaches, and illustrating the
profitable applications.
[Back to top] Right or Left – Enantioselective Catalysis.
New Ni, Pd and Pt Phosphane Complexes with the Chiral 9‑Phenyldeltacyclanyl
Substituent
Henri Brunner
After introducing chirality with the winding columns of baroque altars and snail shells, the enantioselective hydrogenation of dehydroamino acids is described. Then, the enantioselective homo Diels-Alder reaction of norbornadiene with phenylacetylene is presented, which leads to 8‑phenyldeltacyclene in almost enantiomerically pure form. Its reaction with 1,2-bisphosphanylbenzene affords P,P,P’‑tris(9-phenyldeltacyclan-8-yl)-1,2-bisphosphanylbenzene, a chelate ligand with 3 chiral deltacyclanyl substituents and a PH bond, comprising 24 asymmetric carbon atoms of a given configuration and a stereogenic secondary phosphorus atom. This chelate ligand forms mononuclear, phosphido-bridged dinuclear and – most unusual – trinuclear Ni, Pd and Pt complexes. The trinuclear complexes consisting of three joint square planar units are unique in Ni, Pd and Pt chemistry.
[Back to top] Biocatalysis Applied to the Synthesis of Vitamin D Analogues
Susana Fernández, Vicente Gotor-Fernández, Miguel
Ferrero,and Vicente Gotor
It is well
recognized that biocatalysis is of special relevance in organic synthesis.
Among the enzymes used, lipases have demonstrated a great versatility in
enzymatic hydrolysis, transesterification, or aminolysis reactions. Other
biocatalysts, such as oxidoreductases and some liases, are also of interest for
organic chemists to synthesize compounds that are difficult to obtain by classical
chemical procedures. Recently, biotransformations have shown their utility in
natural products synthesis, such as in carbohydrates, steroids and nucleosides.
Vitamin D, through its hormonally active form 1a,25-dihydroxyvitamin
D3, plays an important role in the endocrine
system. This metabolite exhibits a
much broader spectrum of biological activities than expected. As a result, considerable effort has
been made toward the synthesis of structurally related congeners that show
interesting pharmacological applications. Most of the analogues prepared have
modifications on the upper side chain, more accessible from a synthetic point
of view. However, the enzymatic
methodology can simplified the chemical routes allowing the synthesis of
adequate precursors in a most simple way.
We review here, the utility of biotransformations for the preparation of
new Vitamin D analogues using different kind of biocatalysts.
[Back to top] The Synthesis of Disaccharides, Oligosaccharides and Containing Thiosugars
Inmaculada Robina
and Pierre Vogel
Disaccharide and oligosaccharide mimics are potentially
more selective glycosidases inhibitors than simple monosaccharide mimics. They
represent also more selective ligands for lectins and oligosaccharide receptors
and can become immunostimulating agents. The biological properties of
disaccharide and oligosaccharide analogs containing thiosugars
(5-thiopyranoses, 4-thiofuranoses) are revised together with the methods for
their obtention.