New design concepts for constraining glycosylated amino acids

Synthesis of labionin and avionin precursors via a nitrogen-centred-radical-triggered 1,5-HAT reaction of Tris derivatives

Labionin and avionin are non-proteinogenic amino acids containing 2,4-diamino-2-(mercaptomethyl)pentanedioic acid that forms the core structures of spirocyclic peptides including labyrinthopeptin A2 and microvionin, respectively. We have developed a diastereoselective synthetic route to labionin and avionin precursors. This route highlights the formation of the quaternary carbon stereocenter of an α,α-disubstituted amino acid via a regioselective 1,5-HAT reaction of a Tris derivative.

Construction of Quaternary Carbon Stereocenter of α-Tertiary Amine through Remote C-H Functionalization of Tris Derivatives: Enantioselective Total Synthesis of Myriocin

We describe the development of a strategy for the construction of the quaternary carbon stereocenter of α-tertiary amines. This strategy highlights a site-selective C-H functionalization involving an alkoxy-radical-triggered 1,5-hydrogen transfer (1,5-HAT) reaction of a conformationally fixed spiro-compound derived from trishydroxymethylaminomethane (Tris). The utilization of this strategy enabled an enantioselective total synthesis of myriocin, a naturally occurring sphingosine analog that displays potent immunosuppressive activity.

Recent Progress on the Stereoselective Synthesis of Cyclic Quaternary alpha-Amino Acids

The most recent papers describing the stereoselective synthesis of cyclic quaternary alpha-amino acids are collected in this review. The diverse synthetic approaches are classified according to the size of the ring and taking into account the bond that is formed to complete the quaternary skeleton.

Synthesis and spectral properties of cholesterol- and FTY720-containing boron dipyrromethene dyes

Two analogues (1, 2) of free cholesterol and one analogue (3) of the immunosuppressive sphingolipid FTY720 containing a boron dipyrromethene chromophore (BODIPY) were synthesized. The synthetic routes involved preparation of boron dipyrromethene moieties (5, 11), bearing a phenylethynyl group at different positions of the chromophore, and lipids (13, 20) bearing an azido group. The dye was tethered to the lipid via a 1,2,3-triazole in the linker by the click reaction. Analogues derived from 11 [in which an (E)-styrylethynyl moiety is bonded to C-5 of BODIPY] exhibited a marked red shift (approximately 70-80 nm) compared with those derived from 5 (in which a phenylethynyl moiety is bonded to C-8 of BODIPY).

A novel intramolecular hydrogen bonding between a side-chain pyridine ring and an amide hydrogen of the peptide backbone in tripeptides containing the new amino acid, α,α-di(2-pyridyl)glycine

Four tripeptides (Z-AA1-2Dpy-AA3-OMe; AA1, AA3 = Gly, Aib) containing a novel amino acid, alpha, alpha-di(2-pyridyl)glycine (2Dpy), were synthesized by the modified Ugi reaction. NMR analysis clearly indicated that the 2Dpy-containing tripeptides except the peptide in which AA1, AA3 = Aib, adopt a unique conformation with two intramolecular hydrogen bonds between 2Dpy-NH and a pyridine nitrogen and between AA3-NH and another pyridine nitrogen. This conformation has so far not been reported. On the other hand, the peptide Z-Aib-2Dpy-Aib-OMe probably adopts a beta-turn structure which is stabilized by two intramolecular hydrogen bonds between 2Dpy-NH and a pyridine nitrogen and between AA3-NH and the C=O of the Z group.

Stereoselective synthesis of conformationally constrained glycosylated amino acids using an enzyme-catalyzed desymmetrization

As part of an effort to probe the mechanism by which glycosyltransferases recognize glycoproteins and assemble the core structures of O-linked oligosaccharides, constrained glycopeptides, compounds 2 and 3, based on the alpha-N-acetylgalactosaminyl serine substructure 1, were designed. In this paper we describe a stereoselective preparation of protected versions of these compounds. A pig liver esterase-catalyzed enzymatic desymmetrization of a diacetate substrate, 10, was employed as a key component in the synthesis.