Efficient and selective reduction protocols of the 2,2-dimethyl-1,3-benzodioxan-4-one functional group to readily provide both substituted salicylaldehydes and 2-hydroxybenzyl alcohols

Synthesis of (12R,13S)-pyriculariol and (12R,13S)-dihydropyriculariol revealed that the rice blast fungus, Pyricularia oryzae, produces these phytotoxins as racemates

Synthesis of assumed natural (12R,13S)-enantiomers of pyriculariol (1) and dihydropyriculariol (2), phytotoxins isolated from rice blast disease fungus, Pyricularia oryzae, was achieved using Wittig reaction or microwave-assisted Stille coupling reaction as the key step. The synthesis revealed that the natural 1 and 2 are racemates. Foliar application test on a rice leaf indicated that both the salicylaldehyde core and side chain were necessary for phytotoxic activity. The fungus is found to produce optically active phytotoxins when incubated with rotary shaker, but racemic ones when cultured using an aerated jar fermenter.

Synthesis of functionalized benzo[1,3]dioxin-4-ones from salicylic acid and acetylenic esters and their direct amidation

Direct synthesis of 4H-benzo[d][1,3]dioxin-4-one derivatives from salicylic acids and acetylenic esters (both mono- and disubstituted) has been described. The reaction is mediated by CuI and NaHCO₃ in acetonitrile. Room temperature amidation of the synthesized 1,3-benzodioxinones with primary amines readily afforded the corresponding salicylamides in moderate to good yields.

An efficient method for the synthesis of the active core 4H-benzo[d][1,3]dioxin-4-one followed by its direct room temperature amidation is reported.

Highly efficient synthesis of benzodioxins with a 2-site quaternary carbon structure by secondary amine-catalyzed dual Michael cascade reactions

Employing salicylic acids and substituted 3-butyn-2-ones as the substrates, a morpholine catalyzed tandem dual Michael addition afforded a benzodioxin skeleton.

Copper-catalyzed synthesis of benzo[d][1,3]dioxin-4-ones via tandem Ar–halogen bond hydroxylation and dichloromethane-based double Williamson etherification

The copper-catalyzed tandem reactions of o-halobenzoic acids, dichloromethane and KOH giving benzo[d][1,3]dioxin-4-ones via tandem Ar–X hydroxylation and double Williamson etherification are reported.

Oxidative cyclization of alkenoic acids promoted by AgOAc

Alkenoic acids derived from salicylic acid and analogues undergo an unexpected oxidative cyclization process triggered by AgOAc leading to 4H-benzo[d][1,3]dioxin-4-ones. The process is affected by the substitution on the aryl and the allyl units.

A new class of salicylic acid derivatives for inhibiting YopH of Yersinia pestis

Previously, we identified a class of salicylic acid derivatives that display inhibitory activity against the protein tyrosine phosphatase YopH from Yersinia pestis. Because docking study suggested that the large phenyl ring attaching to the salicylic acid core might be exposed to the solvent and might not contribute significantly to binding, we have developed a new class of compounds that no longer contain this phenyl ring. We first devised a synthetic scheme for the compounds and then developed an automated computational screening model surrounding this synthetic scheme to help select a small number of compounds for synthesis and experimental testing. Based on this computational screening model and the analysis of the structure-activity relationship of our previous class of compounds, we have synthesized eight compounds and found five that yield micromolar activity. When applying in a larger scale, the synthetic scheme and the computational screening model developed here should help to identify even more potent inhibitors in the future.

Total synthesis of the aristolochic acids, their major metabolites, and related compounds

Plants from the Aristolochia genus have been recommended for the treatment of a variety of human ailments since the time of Hippocrates. However, many species produce the highly toxic aristolochic acids (AAs), which are both nephrotoxic and carcinogenic. For the purposes of extensive biological studies, a versatile approach to the synthesis of the AAs and their major metabolites was devised based primarily on a Suzuki-Miyaura coupling reaction. The key to success lies in the preparation of a common ring-A precursor, namely, the tetrahydropyranyl ether of 2-nitromethyl-3-iodo-4,5-methylendioxybenzyl alcohol (27), which was generated in excellent yield by oxidation of the aldoxime precursor 26. Suzuki-Miyaura coupling of 27 with a variety of benzaldehyde 2-boronates was accompanied by an aldol condensation/elimination reaction to give the desired phenanthrene intermediate directly. Deprotection of the benzyl alcohol followed by two sequential oxidation steps gave the desired phenanthrene nitrocarboxylic acids. This approach was used to synthesize AAs I-IV and several other related compounds, including AA I and AA II bearing an aminopropyloxy group at position-6, which were required for further conversion to fluorescent biological probes. Further successful application of the Suzuki-Miyaura coupling reaction to the synthesis of the N-hydroxyaristolactams of AA I and AA II then allowed the synthesis of the putative, but until now elusive, N-acetoxy- and N-sulfonyloxy-aristolactam metabolites.

A catalyst-free, facile and efficient approach to cyclic esters: synthesis of 4H-benzo[d][1,3]dioxin-4-ones

A metal and additive free base-mediated method for the formation of 4H-benzo[d][1,3]dioxin-4-one and its derivatives, from salicylic acids and dichloromethane, was developed using dichloromethane (DCM) and 1,1-dichloroethane (1,1-DCE) as the C1 source.

Efficient preparation of α-ketoacetals

The Weinreb amides 2a,b were prepared from the α,α-dimethoxyacetic acids 1c,d. A number of representative nucleophilic additions (RMgX and RLi) on 2 afforded α-ketoacetals 3a–j in 70–99% yield. These compounds represent a versatile arrangement of functional groups of significant synthetic value, as demonstrated in the synthesis of (±)-salbutamol.

Synthesis of arylbromides from arenes and N-bromosuccinimide (NBS) in acetonitrile — A convenient method for aromatic bromination

Regioselective and chemoselective electrophilic bromination of a wide series of activated arenes using N-bromosuccinimide (NBS) in acetonitrile occurs readily. Environmentally friendly conditions, large substrate scope, and ease of synthesis enhance the utility of this method over other electrophilic bromination conditions.

An expedient synthesis of the fibril binding compound FSB via sequential Pd-catalyzed coupling reactions

The styryl benzene derivative (E, E)-1-fluoro-2,5-bis(3-hydroxycarbonyl-4-hydroxy)styrylbenzene (FSB), well-known for its binding to beta-amyloid peptide fibrils, was synthesized in an efficient manner exploiting two sequential palladium(0)-catalyzed coupling reactions in a 34% overall yield. This is a substantial improvement to the previously reported synthesis of FSB in 1.1%.

Total synthesis of anibamine, a novel natural product as a chemokine receptor CCR5 antagonist

The total synthesis of anibamine, the first and only natural product known as a chemokine receptor CCR5 antagonist, is reported herein. Anibamine was synthesized from acetylacetone and cyanoacetamide in 10 steps.