Efficient one-pot synthesis of β-hydroxyphosphonates: regioselective nucleophilic ring opening reaction of epoxides with triethyl phosphite catalyzed by Al(OTf)3

Asymmetric Synthesis of β-Hydroxyphosphonates via a Chemoenzymatic Cascade

Chiral β-hydroxyphosphonates are essential building blocks for organophosphorus compounds. However, the asymmetric synthesis of these units remains a significant challenge. Herein, we describe a one-pot chemoenzymatic cascade process to access chiral β-hydroxyphosphonates, which combines photo-oxidative chemical reactions and bioreductions. The incorporation of photooxidation in the chemical reaction resulted in up to 92% yield and >99% enantiomeric excess (ee) of β-hydroxyphosphonates in the cascade. In addition, the scale-up of diethyl (S)-(2-hydroxy-2-phenylethyl)phosphonate demonstrates the potential application of this strategy.

Boronic acid-catalysed C-3 selective ring opening of 3,4-epoxy alcohols with thiophenols and thiols

In this protocol we described a boronic acid-catalysed C-3 selective ring opening of 3,4-epoxy alcohols with thiophenols and thiols as nucleophiles. This diastereo- and enantiospecific reaction provides an efficient entry to prepare a variety of hydroxyl sulfides. Through the directing effect of the hydroxyl group, nucleophilic attack on the C-3 position of the epoxide moiety is favoured. It can be rationalized in a proposed transition state, in which the boronic acid catalyst tethers both epoxides and S-nucleophiles.

Metal-Catalyzed Directed Regio- and Enantioselective Ring-Opening of Epoxides

Control of regio- and stereoselectivity of chemical reactions is the central theme in synthetic chemistry. Regioselective and enantiospecific ring opening of readily available enantioenriched epoxides precursors provides a straightforward access to diverse highly functionalized molecules which can serve as chiral building blocks for synthesis of biologically active compounds. However, prior to our research work, the scope of catalytic highly regioselective ring opening of epoxides is limited to structurally or electronically biased epoxides, such as terminal and aromatic epoxides. Regioselective ring-opening of epoxides with substituents on both sides demonstrating similar steric and electronic effects is still a formidable challenge for organic chemists. To address this challenge, our approach is to use the readily available functional moiety incorporated in an epoxide as a directing group to realize the regioselective nucleophilic attack on the oxirane ring. Alternatively, asymmetric ring-opening of epoxides can also provide the ring-opening products in highly enantioenriched form. However, excellent results are usually obtained in the case of the kinetic resolution of terminal epoxides or the desymmetrization of meso-epoxides. In these cases, the issue of regiocontrol of the ring-opening is circumvented or minimized. Based on our successful results of regioselective ring-opening of functionalized epoxides by implementing the directed ring-opening strategy, we also investigated the enantioselective ring-opening of internal epoxides bearing a functional moiety as directing group. This Account summarizes our research on metal-catalyzed directed ring-opening reactions of epoxides, which encompasses the following breakthroughs: (1) highly regioselective ring-opening of various substrates including epoxy allylic alcohols, epoxy homoallylic alcohols and epoxy allylic sulfonamides with a variety of N-, O-, and halide-nucleophiles catalyzed by W-, Mo-, or Ni-salt; (2) first kinetic resolutions of epoxy allylic alcohols, epoxy homoallylic alcohols, and epoxy allylic sulfonamides with various amines as nucleophiles, which were catalyzed by W-bishydroxamic acid (W-BHA), nickel-BINAM, and Gd-N,N'-dioxide catalytic system, respectively; (3) successful implementation of the strategy of combined asymmetric syntheses by the combination of the enantioselective epoxidation and the enantioselective ring-opening of 2,3-epoxy alcohols establishing a new entry to prepare amino alcohols in regio-, diastereo-, and enantiomerically pure form.

Synthesis and antiproliferative activity of novel α- and β-dialkoxyphosphoryl isothiocyanates

A series of 15 mostly new dialkoxyphosphoryl alkyl and aralkyl isothiocyanates were synthesized using two alternative strategies, and their in vitro antiproliferative activity against several cancer cell lines (including drug resistant) is here demonstrated. The IC(50) values measured for the new compounds are within the range of 6.3-21.5 μM, and they are quite similar to the activity of two best and most extensively investigated natural benzyl isothiocyanate (A) and phenethyl isothiocyanate (B). Preliminary studies utilizing the cell cycle and reduced glutathione level analysis performed on A549 lung cancer cell line using representative compounds revealed important differences in the mechanism of action possibly correlated with their chemical properties. Hydrophobic compounds react mainly with the cytosolic glutathione reduced leading to its depletion, causing an oxidative stress and cell cycle arrest in G0/G1 phase. On the other hand, hydrophilic compounds cause moderate cell cycle arrest and massive cell death associated with moderate reduced glutathione depletion. These suggest that significant changes in the chemical structure of isothiocyanates, which do not lead to the significant changes in antiproliferative activity, but simultaneously cause a differences in the mechanism of action are possible.