Total Synthesis of Cyclomarin C

The total synthesis of cyclomarin C was accomplished through a convergent strategy from a tetrapeptide fragment and a tripeptide one. The developed methods to prepare the needed noncoded amino acids, the proper protection of peptide fragments, and identification of the optimum macrocylization site can be applied to further synthetic studies on other members of cyclomarins

Biomimetic Total Syntheses of Cassiarins A and B

Total syntheses of cassiarins A and B have been efficiently accomplished using a common strategy with biomimetic considerations. Key reactions involved in this synthesis include a Negishi-type coupling, a Ag(I)-promoted formation of the tricyclic 8H-pyrano[2,3,4-de]chromen-8-one core, and a sequential amine-condensation and cyclization. Three new analogues of cassiarin A bearing different substituents at the C-11 position were synthesized in parallel from the same intermediate. In addition, two other transformations to the key tricyclic cores and cassiarins A and B were achieved from corresponding chemically equivalent precursors

Total Synthesis of Cyclomarin C

The total synthesis of cyclomarin C was accomplished through a convergent strategy from a tetrapeptide fragment and a tripeptide one. The developed methods to prepare the needed noncoded amino acids, the proper protection of peptide fragments, and identification of the optimum macrocylization site can be applied to further synthetic studies on other members of cyclomarins

Ring-Closing Metathesis-Based Synthesis of (3<i>R</i>,4<i>R</i>,5<i>S</i>)-4-Acetylamino-5-amino-3-hydroxy- cyclohex-1-ene-carboxylic Acid Ethyl Ester: A Functionalized Cycloalkene Skeleton of GS4104

(3R,4R,5S)-4-Acetylamino-5-amino-3-hydroxy-cyclohex-1-ene-carboxylic acid ethyl ester, a functionalized cyclohexene skeleton of GS4104, was diastereoselectively synthesized. A major advantage of this synthesis is the use of readily available l-serine to replace frequently used (−)-shikimic acid or (−)-quinic acid as the starting material. Ring-closing metathesis and diastereoselective Grignard reactions successfully served as the key steps. Absolute configurations of the key intermediates were confirmed by corresponding two-dimensional NMR studies

Total Synthesis of Cyclomarin C

The total synthesis of cyclomarin C was accomplished through a convergent strategy from a tetrapeptide fragment and a tripeptide one. The developed methods to prepare the needed noncoded amino acids, the proper protection of peptide fragments, and identification of the optimum macrocylization site can be applied to further synthetic studies on other members of cyclomarins

Synthesis Studies toward Chloroazaphilone and Vinylogous γ-Pyridones: Two Common Natural Product Core Structures

Chloroazaphilone is a common structure found in a number of natural products. Reported herein is a practical synthesis of a model chloroazaphilone that utilizes Pb(OAc)4 oxidation of HClO4/HOAc pyrinium salt in a key one-pot operation. Reaction of this chloroazaphilone with various primary amines to afford the corresponding vinylogous γ-pyridones was also fully investigated. The isolation of stable enamine intermediates provided direct evidence of reaction mechanisms

Synthesis Studies toward Chloroazaphilone and Vinylogous γ-Pyridones: Two Common Natural Product Core Structures

Chloroazaphilone is a common structure found in a number of natural products. Reported herein is a practical synthesis of a model chloroazaphilone that utilizes Pb(OAc)4 oxidation of HClO4/HOAc pyrinium salt in a key one-pot operation. Reaction of this chloroazaphilone with various primary amines to afford the corresponding vinylogous γ-pyridones was also fully investigated. The isolation of stable enamine intermediates provided direct evidence of reaction mechanisms

RCM Approaches toward the Diastereoselective Synthesis of Vicinal <i>trans</i>-Diaminocyclitols from l-Serine

Starting from l-serine, the asymmetric synthesis of four diaminocyclitol derivatives as sugar-based glycosidase inhibitors has been achieved using ring-closing metathesis (RCM) as a key step. Introduction of vicinal trans-diamino functionality onto the acyclic precursors was accomplished by highly diastereoselective addition of Grignard reagent to imine, and the elaboration of polyhydroxylic groups was effected via diastereoselective olefin epoxidation or dihydroxylation. The absolute configurations of final products were confirmed by 2D NMR studies

Synthesis of a New Conformation-Constrained l-Tyrosine Analogue as a Potential Scaffold for SH2 Domain Ligands

The enantioselective synthesis of a new tricyclic tyrosine analogue is reported. This conformation-contrained SH2 domain ligand scaffold 2 was designed on the basis of the natural ligand, whose structure contains the elements of a tyrosine moiety having χ1 and χ2 angles constrained to values observed for a phosphotyrosyl (pTyr) residue bound to the p56lck SH2 domain. It represents a unique, highly constrained amino acid, which may be of value in signal transduction studies. Three key steps, an asymmetric tandem Michael addition, an intramolecular Friedel−Crafts reaction, and an intramolecular Mannich reaction, were successfully applied in the presented synthetic route

Asymmetric Annulation of 3‑Alkynylacrylaldehydes with Styrene-Type Olefins by Synergetic Relay Catalysis from AgOAc and Chiral Phosphoric Acid

Asymmetric annulation of 3-alkynylacrylaldehydes with 2-hydroxystyrenes has been studied and achieved by synergetic catalysis from AgOAc and chiral phosphoric acid, providing the corresponding multiring products with decent total yields and moderate to excellent enantioselectivities (up to 95% ee). The developed mild multibond-formation cascade reaction involves in situ generation of pyrylium intermediate by Ag­(I)-catalyzed alkyne/carbonyl cycloisomerization, counteranion-directed asymmetric oxa [4 + 2]-cycloaddition, and intramolecular nucleophilic substitution