Solid-Phase Total Synthesis of Plusbacin A3

The total synthesis of the depsipeptide natural product plusbacin A₃ (1) utilizing solid-phase peptide synthesis (SPPS) was disclosed. A 3-hydroxy-proline derivative compatible with Fmoc SPPS was prepared by a diastereoselective Joullié-Ugi three-component reaction (JU-3CR)/hydrolysis sequence. After peptide elongation on the solid support, cleavage of the peptide from the resin, followed by macrolactamization and global deprotection, gave plusbacin A₃ (1).

Diastereoselective synthesis of new zwitterionic bicyclic lactams, scaffolds for construction of 2-substituted-4-hydroxy piperidine and its pipecolic acid derivatives

The synthesis of new chiral highly functionalized zwitterionic bicyclic lactams starting from acyclic β-enaminoesters derived from (R)-(-)-2-phenylglycinol is described. The key step involved an intramolecular non-classical Corey-Chaykovsky ring-closing reaction of the corresponding sulfonium salts derived from β-enaminoesters. This methodology permits the generation of two or three new stereogenic centers with high diastereoselectivity. The utility of these intermediates was demonstrated by the stereocontrolled total synthesis of cis-4-hydroxy-2-methyl piperidine and its corresponding pipecolic acid derivative.

The endo-aza-Michael addition in the synthesis of piperidines and pyrrolidines

Intramolecular endo-aza-Michael additions are categorised in various ways.

Phosphorus-containing amino acids with a P–C bond in the side chain or a P–O, P–S or P–N bond: from synthesis to applications

Strategies for the preparation of phosphorus-containing amino acids and their utility in the organic chemistry, physico-chemistry, agrochemistry, and pharmacology fields are reported.

Conformationally rigid pyrazoloquinazoline α-amino acids: one- and two-photon induced fluorescence

Conformationally rigid unnatural α-amino acids bearing a pyrazoloquinazoline ring system that are amenable to both one- and two-photon excitation have been developed as new fluorescent probes.

Stereoselective synthesis of 2,6-trans-4-oxopiperidines using an acid-mediated 6-endo-trig cyclisation

An acid-mediated 6-endo-trig cyclisation of amine-substituted enones has been developed for the stereoselective synthesis of trans-6-alkyl-2-methyl-4-oxopiperidines. Performed under conditions that prevent removal of the Boc-protecting group or acetal formation, the key cyclisation was found to generate cleanly the 4-oxopiperidine products in high overall yields from a wide range of alkyl substituted enones. The synthetic utility of the trans-6-alkyl-2-methyl-4-oxopiperidines formed from this process was demonstrated with the total synthesis of the quinolizidine alkaloid, (+)-myrtine and the piperidine alkaloid, (-)-solenopsin A.

Access to 2,6-Disubstituted 4-Oxopiperidines Using a 6-Endo-trig Cyclization: Stereoselective Synthesis of Spruce Alkaloid and (+)-241D

A synthetic route to cis-2-methyl-4-oxo-6-alkylpiperidines has been developed using a 6-endo-trig cyclization of (E)-enones. The base-mediated intramolecular cyclization was found to be general for both alkyl- and aryl-substituted enones, providing the corresponding 4-oxopiperidines in high yields (80-89%). Stereoselective reduction of the 2,6-cis-disubstituted 4-oxopiperidines then gave the 2,4,6-cis,cis-trisubstituted 4-hydroxypiperidines in high diastereoselectivity. The general nature of this approach was demonstrated with the synthesis of the natural products, spruce alkaloid and (+)-241D.

Synthesis of pyrazole containing α-amino acids via a highly regioselective condensation/aza-Michael reaction of β-aryl α,β-unsaturated ketones

A new class of α-amino acid incorporating 5-aryl pyrazole units have been prepared using a highly regioselective condensation/aza-Michael reaction of β-aryl α,β-unsaturated ketones.

A concise diastereoselective approach to enantioenriched substituted piperidines and their in vitro cytotoxicity evaluation

A library of diversely stereo-oriented, highly substituted 2,6-cis piperidine derivatives were synthesized, and evaluated for their anticancer activity in cancer cells that included A549 (lung cancer, CCL-185), MCF7 (breast cancer (HTB-22), DU145 (prostate cancer (HTB-81), and HeLa (cervical cancer, CCL-2). One stereo-variant emerged as a promising candidate for further design based structure-activity studies.

Stereoselective synthesis of unsaturated and functionalized L-NHBoc amino acids, using Wittig reaction under mild phase-transfer conditions

The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the γ-iodo NHBoc-amino ester, derived from L-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid-liquid phase-transfer conditions in chlorobenzene and in the presence of K(3)PO(4) as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with substituted aldehydes allows to graft various functionalized groups on the lateral chain of the amino acid, such as trifluoromethyl, cyano, nitro, ferrocenyl, boronato, or azido. In addition, the reaction of the amino acid Wittig reagent with α,β-unsaturated aldehydes leads to amino acids bearing a diene on the lateral chain. Finally, this amino acid phosphonium salt appears to be a new powerful tool for the preparation of unsaturated and non-proteinogenic α-amino acids, directly usable for the synthesis of customized peptides.