Shengping Zheng

Bioactive and marker compounds from two edible dark-colored Myrciaria fruits and the synthesis of jaboticabin.

Jaboticaba (Myrciaria cauliflora) and false jaboticaba (Myrciaria vexator) fruits are two pleasant-tasting, dark-colored fruits, native to Brazil. They are rich sources of phenolic compounds, including anthocyanins, flavonoids, phenolic acids, and tannins, as well as less well known polyphenols such as depsides. These two fruits are very similar in morphology, but their taste profiles differ markedly. This study was focused on identifying the marker compounds between them using HPLC-PDA and LC-TOF-MS, combined with principal component analysis. As a result, cyanidin-3-O-glucoside was found as the major anthocyanin in Myrciaria fruits. Delphinidin-3-O-glucoside was found to be the marker compound for jaboticaba, while cyanidin-3-O-galactoside and cyanidin-3-O-arabinose were two marker compounds distinguishing false jaboticaba. In addition, two ellagitannins, iso-oenothein C and oenothein C, were isolated and identified from both of these fruits for the first time. Jaboticabin, a minor bioactive depside, occurred in both fruits and, because of its potential to treat chronic obstructive pulmonary disease, was successfully synthesized in the laboratory.

Cobalt-Catalyzed α-Alkylation of Ketones with Primary Alcohols

An ionic cobalt-PNP complex is developed for the efficient α-alkylation of ketones with primary alcohols for the first time. A broad range of ketone and alcohol substrates were employed, leading to the isolation of alkylated ketones with yields up to 98%. The method was successfully applied to the greener synthesis of quinoline derivatives while using 2-aminobenzyl alcohol as an alkylating reagent.

Assembling mono-, di- and tri-nuclear coordination complexes with a ditopic analogue of 2,2′:6′,2′′-terpyridine: syntheses, structures and catalytic studies

4-Phenyl-2,6-bis(2′-pyrazinyl)pyridine (L) as a closely related ditopic analogue of 2,2′:6′,2′′-terpyridine, was synthesized through a facile one-pot Krohnke condensation, along with the structural determination of transition metal coordination assemblies of this ditopic ligand. A variety of metal complexes including mono-, di- and tri-nuclear structures 1–6 were revealed, dependent upon the metal salts and reaction conditions employed. Although reactions of L with copper(II) or zinc(II) nitrates and zinc(II) iodide gave only simple mononuclear mono-ligand complexes, that using cobalt thiocyanate led to a dinuclear dimeric complex. The potential of outer N-donors of the ligand backbone in extending mononuclear complexes into polynuclear assemblies was further investigated. The solution reaction of [Fe(L)2]2+ species with CoII gave an ionic complex containing [Co(SCN)4]2− counterions, leaving the outer pyrazinyl-N non-coordinated. However, the solvothermal assembly of L with copper(II) chloride facilitates the formation of a discrete trinuclear complex via outer-N coordination, indicating the promising applications of L in constructing complicated supramolecular structures. Catalytic tests were carried out on copper(II)- and cobalt(II)-containing complexes 1 and 4–6 for the aerobic alcohol oxidation. Up to 99% conversion of benzylic alcohol to benzaldehyde was observed when 1 (1 mol%) was used as a catalyst, in the presence of TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) and DMAP (4-dimethylaminopyridine) in acetonitrile, while the trinuclear 6 was a better catalyst when the reaction was conducted in water.

A Variation of the Fischer Indolization Involving Condensation of Quinone Monoketals and Aliphatic Hydrazines

The indole ring system is one of the most ubiquitous heterocycles in nature. Many indole-containing natural products show a wide scope of biological activities, in particular because they bind to many receptors with high affinity. Since Baeyer s first synthesis of indole from oxindole in 1866 (indigo!isatin!oxindole!indole), numerous methods for the synthesis of indoles have been reported. One of the most efficient and widely employed syntheses is the Fischer indolization discovered in 1883. Compared with other indole syntheses, the importance of Fischer indolization lies in its simplicity and convenience, that is, formation of a critical C C bond to an unactivated aromatic carbon through a [3,3] sigmatropic rearrangement of enolizable Narylhydrazones. After more than a century of development, the Fischer indole synthesis remains a reliable and versatile method for the preparation of a variety of indole natural products and medicinal compounds. Many new variations have been developed in recent years. Most recently, the first catalytic asymmetric version of Fischer indole synthesis was reported by the group of List. Although the Fischer indole synthesis is widely used, several disadvantages still remain. The classical Fischer indole synthesis starts with arylhydrazines, which are generally made either from anilines through diazonium salts, or from aryl halides through transitionmetal-mediated coupling reactions. These processes involve the use of aniline precursors and toxic reagents (nitrous acid, stannous chloride, etc.) and potentially explosive diazonium intermediates, or expensive transition metals. We report herein a novel variation of the Fischer indolization involving a one-pot condensation of quinone monoketals with aliphatic hydrazines (Scheme 1). To the best of our knowledge, this is the first Fischer-type indole synthesis using an aliphatic hydrazine as the nitrogen source and a quinone monoketal as a masked benzene ring. We envisioned that condensation of quinone monoketal 1 and aliphatic hydrazine 2 would ultimately lead to an indole via alkylaryldiazene 5 and arylhydrazone intermediate 6, as illustrated in Scheme 2. The feasibility of this method relies on the initial formation of alkylaryldiazene 5 from a 1,2addition/dehydration sequence. It should be noted that there has been no report on the synthesis of alkylaryldiazenes 5 from quinone derivatives and aliphatic hydrazines, although arylaryldiazenes (azobenzenes) have been synthesized from condensations of arylhydrazines with quinones, quinols, quinone monoketals, and quinone bisketals. There is a single report on the condensation of an aliphatic hydrazine (N,N-dimethylhydrazine) with naphthoquinone monoketal, which, however, gave a 1,4-addition product in high yield. Therefore, our first object was to test the practicality of the Scheme 1. Strategies for the synthesis of indoles.

Double Hetero-Michael Addition of N-Substituted Hydroxylamines to Quinone Monoketals: Synthesis of Bridged Isoxazolidines

A general synthesis of bridged isoxazolidines from a double hetero-Michael addition of N-substituted hydroxylamines to quinone monoketals has been developed. The different addition order of N-benzylhydroxylamine and N-Boc hydroxylamine is also discussed. Moreover, the various functionalities in the isoxazolidine products allow facile derivatization.

An expedient stereoselective and chemoselective synthesis of bicyclic oxazolidinones from quinols and isocyanates

A mild and efficient synthesis of bicyclic oxazolidinones from quinols and isocyanates, under DBU-mediated conditions at room temperature, is described. The aza-Michael addition to substituted cyclohexadienones is stereoselective and chemoselective.

Synthesis of o-chlorophenols via an unexpected nucleophilic chlorination of quinone monoketals mediated by N,N′-dimethylhydrazine dihydrochloride

An unexpected nucleophilic chlorination of a quinone monoketal while carrying out a pyrazolidine synthesis has led to a general preparation of multisubstituted phenols. The products are obtained in good to high yields under mild conditions. The bridged pyrazolidines that were the original targets are obtained in the presence of a protic solvent.

Cobalt(II) Coordination Polymer as a Precatalyst for Selective Hydroboration of Aldehydes, Ketones, and Imines

Highly effective hydroboration precatalyst is developed based on a cobalt(II)-terpyridine coordination polymer (CP). The hydroboration of ketones, aldehydes, and imines with pinacolborane (HBpin) has been achieved using the recyclable CP catalyst in the presence of an air-stable activator. A wide range of substrates containing polar C═O or C═N bonds have been hydroborated selectively in excellent yields under ambient conditions.