Total synthesis of ningalin D

A concise (nine-step) and effective (19% overall yield) total synthesis of ningalin D (1a) is disclosed and is based on a key 1,2,4,5-tetrazine --> 1,2-diazine --> pyrrole Diels-Alder strategy to assemble a fully substituted pyrrole core central to its structure. Additional highlights of the synthesis include a double Dieckmann condensation to introduce the C and D aryl rings enlisting substituents judiciously placed on the dienophile and intrinsic to the widely used tetrazine 2, a highly effective Suzuki coupling of the resulting C and D phenol triflates for introduction of the sterically demanding F and G aryl rings, and an unusually effective formal oxidative decarboxylation reaction cascade initiated by a Curtius rearrangement to directly provide the biphenylene quinone methide found imbedded in the structure of ningalin D. The cytotoxic and multidrug resistance (MDR) reversal activity of ningalin D, its derivatives, and the key synthetic intermediates are detailed.     

Total synthesis of lamellarins D, H, and R and ningalin B

A concise total synthesis of lamellarins D (7 steps), H (7 steps), and R (5 steps) and ningalin B (5 steps) is achieved starting from the corresponding aldehydes and amines. The synthesis features three oxidative reactions as key steps in a biomimetic manner, involving an AgOAc-mediated oxidative coupling reaction to construct the pyrrole core, a Pb(OAc)(4)-induced oxidative cyclization to form the lactone, and Kita's oxidation reaction to form the pyrrole-arene C-C bond.     

Regioselective preparation of 2-substituted 3,4-diaryl pyrroles: a concise total synthesis of ningalin B

Methylisocyanoacetate undergoes a 2 + 3 cycloaddition with alpha,beta-unsaturated nitriles to provide a regioselective synthesis of 2-substituted 3,4-diaryl pyrroles. The ease of preparation of alpha,beta-unsaturated nitriles allows the rapid synthesis of pyrroles with varied substituents. Using this method, a key intermediate (1) for the synthesis of the marine natural products lukianol A, lamellarin O, and lamellarin Q was prepared in two steps. A total synthesis of ningalin B (11) was also accomplished utilizing this methodology.     

Efficient synthesis of H & C labeled benzaldehydes via regio-selective formylation

Benzaldehydes are important building blocks in synthetic organic chemistry that have wide applications for the synthesis of natural products and pharmaceutical drugs. Herein we report a general synthetic methodology for the synthesis of highly functionalized ²H and ¹³C labeled benzaldehydes in transfer of isotopic purity >99% via regio-selective formylation. Regio-selective deprotonation of substituted benzene 1 with LDA/n-BuLi at −78 °C and treatment with DMF-d₇ or EtO-¹³CHO led to the synthesis of 2-deutero-1,3-disubstituted benzaldehydes 2/4 in moderate to good yields. The synthetic methodology described represents a simple yet versatile route to functionalized formyl-deuterated, tritiated ¹³C and ¹⁴C labeled benzaldehydes.     

Efficient synthesis of scutellarein

Scutellarein is a component of Scutellaria, recently known as a potent cytotoxic agent on human leukaemia cells. The aim of this study was the synthesis of scutellarein and its methylated derivative. The new features are the innovating method to afford flavones from flavanones and the A-ring regioselective bromination step that lead to the target molecule by a facile and high-yielding pathway.     

Efficient synthesis of thiazoloquinazolinone derivatives

An original route to the rare 8H-thiazolo[5,4-f]quinazolin-9-one 1 and the novel 7H-thiazolo[4,5-h]quinazolin-6-one 2 is described. Access to the regioisomers was realized by fusion of a thiazole and a quinazoline ring via Appel's salt chemistry. Thermal reactions were carried out using a focused microwave reactor, reducing the overall time of the multi-step synthesis.     

Efficient synthesis of 2'-C-beta-methylguanosine

2'-beta-Methyl nucleosides have potential value as therapeutic agents and as nucleoside analogues for exploring RNA biology. Here we develop a strategy for efficient synthesis for 2'-C-beta-methylguanosine (3). Starting from 1,2,3,5-tetra-O-benzoyl-2-C-beta-methyl-d-ribofuranose (1) and N2-acetylguanine, we obtained the title compound in two steps (78% overall yield) with high stereoselectivity (beta/alpha > 99:1) and high regioselectivity (N9/N7 > 99:1). Extension of this strategy to the classic synthesis of guanosine also resulted in high stereoselectivity (beta/alpha = 99:1) and improved regioselectivity (N9/N7 = 97:3).     

Efficient synthesis of unsymmetrical disulfides

A novel way of synthesizing unsymmetrical disulfides from thiols with DDQ is presented here. This procedure ran in a straightforward manner to give high product yields. Unsymmetrical disulfides were directly synthesized from the corresponding mixture of thiols in equimolar amounts under mild conditions.     

C, O, S, N-苷的高效立体选择合成

研究了正氟乙酸糖苷和三甲基硅烷基糖苷醚作为糖苷给予体。在路易士酸存在时应用1-O-三氟乙酰基-2,3,4,6-四-O-苄基-α-D-吡喃葡萄糖和芳香醚合成C-芳基-D-吡喃葡萄糖苷的方法。在十分温和的条件下以81-99%的得率获得β-异构体, 这一方法被扩展到O, S, N-苷的合成。     

Efficient synthesis of substituted dihydrotetraazapentacenes

We describe a versatile and very efficient synthesis of previously unknown substituted 5,14-dihydro-5,7,12,14-tetraazapentacenes (DHTAPs). A structural study by NMR spectroscopy showed that the conjugated pi-system of the pentacyclic skeleton rearranges depending on the electronic effect of the substituent(s).     

Efficient synthesis of spiroisoxazoline oxindoles

The synthesis of spiroisoxazoline oxindoles containing ester groups at position 4′ and aromatic or ester groups at position 3′ of the isoxazoline ring is reported. The compounds were synthesized in yields up to 94% by 1,3-dipolar cycloaddition of 3-methylene indolin-2-ones and chlorooximes in the presence of triethylamine or zinc.     

Efficient synthesis of cyclopropylhydrazine salts

An efficient procedure for the synthesis of cyclopropylhydrazine in the form of its salts is reported. The copper salt-catalyzed addition of cyclopropylboronic acid to the azo group of di-tert-butyl azodicarboxylate and subsequent deprotection gave the cyclopropylhydrazine salts in high yields.     

Efficient BOP-mediated synthesis of fulgimides

A mild and efficient method for the synthesis of fulgimides is presented in which the peptide coupling reagent BOP is employed for dehydratation of fulgenic acid monoamides (succinamic acids). The disclosed method proved to be superior to those described in the literature.     

Efficient synthesis of naphthodiazacrown ethers

A benign and efficient synthesis of naphthodiazacrown ethers has been described. Reaction of simple dialdehyde precursor with α,ω-diamines followed by sodium borohydride reduction leads to 16-27 membered naphthodiazacrown ethers in 80-90% yields.     

Efficient synthesis of carbohydrate thionolactones

Carbohydrate thionolactones may be efficiently synthesized from the corresponding 1-thio sugars via a two-step procedure involving formation of a glycosyl phenylthiosulfinate by treatment with either phenylsulfinyl chloride or 1-(phenylsulfinyl)piperidine (BSP), and subsequent thermal elimination in toluene.     

Efficient solid-phase synthesis of sulfahydantoins

A novel solid-phase strategy allows the efficient preparation of "traceless" sulfahydantoins. A total of 28 derivatives, with crude purity generally higher than 85%, were prepared by parallel synthesis. Through reductive alkylations, Mitsunobu reactions, and sulfamoylation reactions on oxime resin, the synthetic strategy affords sulfahydantoin derivatives selectively substituted at N(2), N(5) and N(2), N(5) positions, although yields of disubstituted compounds are lower. The mild reaction conditions involved lead to sulfahydantoins without racemization.     

Efficient synthesis of alkyl beta-diketimines

A general synthesis for the preparation of alkyl N,N'-beta-diketimines has been developed. The method reported here demonstrates the use of dimethyl sulfate for conversion of enaminoketones to beta-diketimines. The reaction can be performed without solvent, providing good yields.     

Efficient synthesis of the C(1)-C(9) fragment of amphidinolides C, C2, and F

The synthesis of the C(1)-C(9) fragment of amphidinolides C, C2, and F was achieved by using a vinyloguous Mukaiyama aldol reaction on a chiral aldehyde with a silyloxyfuran and by using a C-glycosylation of a lactol derivative with an acetyl oxazolidinethione. From the available chiral acetonide-glyceraldehyde, all the stereogenic centers were perfectly induced along the synthesis. The C(1)-C(9) fragment was synthesized as a vinyl stannane at C(9) in 10 steps, with 16% yield.     

Efficient and diversity-oriented total synthesis of Riccardin C and application to develop novel macrolactam derivatives

Riccardin C (RC, 1) is a macrocyclic bis(bibenzyl) natural product exhibiting remarkable biological activity as a nuclear liver X receptors (LXRs) ligand and a lipid metabolism mediator. RC is expected to be a lead compound to develop drugs for atherosclerotic diseases, and therefore exploiting diversity-oriented synthesis of RC is a promising approach to drug discovery. In this paper, we report novel total synthesis of RC (7.4% overall yield in 16 steps) by using the intramolecular S_NAr reaction as key cyclization reaction. This is the first example of efficient macrocyclization using 3-nitro-4-fluorostilbene as an electrophile. The methodology could be applied to synthesize novel lactam analogs of RC. The diversity-oriented synthesis of RC is versatile method for the synthesis of various types of bis(bibenzyl) natural products and their derivatization.     

Efficient one-pot synthesis of glycosyl disulfides

Methodology for the efficient and facile synthesis of glycosyl disulfides is reported. A one-pot procedure employing mild conditions using diethyl azodicarboxylate is described to synthesise a series of glycosyl disulfides in excellent yields.