Convenient Synthesis of Cyclopropylalkanol Derivatives Possessing a Difluoromethylenephosphonate Group at the Ring

Access to cyclopropanes with geminal trifluoromethyl and difluoromethylphosphonate groups

A synthetic route to the bench-stable fluorinated masked carbene reagent diethyl 2-diazo-1,1,3,3,3-pentafluoropropylphosphonate, bearing a trifluoromethyl and a difluoromethyl group is reported for the first time. Its application in CuI-catalyzed cyclopropanation reactions with aromatic and aliphatic terminal alkenes under mild reaction conditions is demonstrated. In total, sixteen new cyclopropanes were synthesized in good to very good yields.

Development of Biologically Active Compounds on the Basis of Phosphonic and Phosphinic Acid Functionalities

Phosphonic and phosphinic acids, especially α-heteroatom-substituted ones, possess unique structural and physical features which enable them to act as hydrotically stable analogs to biological phosphates in biological processes. They also act as mimetics in the transition state of the protease-induced hydrolysis of dipeptides. The first half of this review focuses on selected new synthetic methods developed by our research group for the stereoselective synthesis of α-heteroatom-substituted phosphonic and phosphinic acid derivatives, including modified nucleotide analogs and phosphinyl dipeptide isosteres. In the latter half, this review summarizes the utility of difluoromethylenephosphonic acids and phosphonic acid esters in the development of enzyme inhibitors against protein tyrosine phosphatases, sphingomyelinases, purine nucleoside phosphorylases and thrombin. The enzyme inhibitors developed were used as probes to elucidate signal transductions and the mechanisms of enzyme actions. The findings of the studies are briefly described.

From Peptides to Peptidomimetics: A Strategy Based on the Structural Features of Cyclopropane

Peptidomimetics, non-natural mimicries of bioactive peptides, comprise an important class of drug molecules. The essence of the peptidomimetic design is to mimic the key conformation assumed by the bioactive peptides upon binding to their targets. Regulation of the conformation of peptidomimetics is important not only to enhance target binding affinity and selectivity, but also to confer cell-membrane permeability for targeting protein-protein interactions in cells. The rational design of peptidomimetics with suitable three-dimensional structures is challenging, however, due to the inherent flexibility of peptides and their dynamic conformational changes upon binding to the target biomolecules. In this Minireview, a three-dimensional structural diversity-oriented strategy based on the characteristic structural features of cyclopropane to address this challenging issue in peptidomimetic chemistry is described.

Rh-catalyzed Negishi alkyl-aryl cross-coupling leading to alpha- or beta-phosphoryl-substituted alkylarenes

The catalytic cross-coupling between ArZnX and ICH(2)(CH(2))(n)P(O)(OEt)(2) (n = 0-3) has been investigated to determine the utility of the Rh catalyst during the alkyl-aryl cross-coupling and to develop a new synthetic method for phosphoryl-substituted alkylarenes. Rh-dppf exhibits an excellent catalytic activity for the reaction with the alkylphosphonate of n = 1, whereas for the reaction with those of n = 2 or 3, beta-hydride elimination mainly takes place. As for the reaction with an alkylphosphonate of n = 0, a polarity inversion of the coupling components is necessary in order to provide the coupling products; the phosphoryl analogue of the Reformatsky reagent and ArI give the cross-coupling products in good yields through the catalysis by Rh-dppf.

Phosphonodifluoromethyl and Phosphonothiodifluoromethyl Radicals. Generation and Addition onto Alkenes and Alkynes

[reaction: see text] Selanylated difluoromethylphosphonates and difluoromethylphosphonothioates are good precursors to phosphonodifluoromethyl and phosphonothiodifluoromethyl radicals, respectively. When generated in the presence of alkenes and a hydrogen donor, the corresponding alpha,alpha-difluorinated alkylphosphonates or alkylphosphonothioates are produced in fair to good yields. The use of alkynes results in the formation of alpha,alpha-difluorinated allyl derivatives in useful yields. The presence of the sulfur atom in phosphonothiodifluoromethyl radicals usually translates into higher isolated yields.

The preparation of new phosphorus-centered functional groups for modified oligonucleotides and other natural phosphates

Efforts to develop synthetic methodologies allowing the preparation of alpha,alpha- difluorophosphonothioates, alpha,alpha-difluorophosphonodithioates, alpha,alpha-difluorophosphono- trithioates, and alpha,alpha-difluorophosphinates are reviewed in the light of applications in the field of modified oligonucleotides and cyclitol phosphates. Two successful approaches have been developed, based either on the addition of phosphorus-centered radicals onto gem-difluoroalkenes or on a process involving the addition of lithiodifluorophosphono- thioates 91 onto a ketone and the subsequent deoxygenation reaction of the adduct. The radical route successfully developed a practical route to alpha,alpha-difluoro-H-phosphinates which proved to be useful intermediates to a variety of phosphate isosters. The ionic route led to the first preparation of phosphonodifluoromethyl analogues of nucleoside- 3'-phosphates.

[Synthesis of phosphonic acid and phosphinic acid derivatives for development of biologically active compounds]

This paper covers recent publications from our laboratory on the synthesis of a variety of phosphonate and phosphinate derivatives. New methods for the enantioselective synthesis of alpha-hydroxyphosphonates were established by Lewis acid-mediated cleavage of homochiral 1,3-dioxaneacetals with P(OEt)(3) and chiral metal ligand-mediated hydrophosphonylation of aldehydes. Two diastereomers of HPmp derivatives were prepared by an application of these methods. The HPmp derivatives were convered to FPmp derivatives but with low diastereoselectivity. Hydrophosphonylation of alpha-aminoaldehydes afforded threo- and erythro-beta-amino-alpha-hydroxyphosphonates under chelation and nonchelation controlled conditions, respectively. The asymmetric dihydroxylation of alpha, beta-, and beta, gamma-unsaturated phosphonates with AD-mix-alpha and AD-mix-beta reagents gave alpha, beta- and beta, gamma-dihydroxyphosphonates with high enantioselectivity. The method was applied to the kinetic resolution of racemic alpha-oxygetated beta, gamma-unsaturated phosphonates. Treatment of allyloxymethylphosphonates with the base afforded alpha-hydroxyphosphonates via the [2,3]-Wittig reaction. Threo- and erythro-beta-amino-alpha-hydroxyphosphinates were obtained with high diastereoselectivity by phosphinylation of alpha-aminoaldehydes in the presence of (R)- and (S)-ALB, respectively. The phosphinylation of alpha-oxygenated aldehydes afforded the corresponding alpha, beta-dioxygenated phosphinates, but with low diastereoselectivity. Sphingomyelin analogues containing CF(2)PO(OH)(2) were synthesized starting from (S)- and (R)-Garner aldehyde for the purpose of obtaining potent sphyngomyelinase inhibitors. A useful method for the synthesis of alpha, alpha-difluorobenzylphosphonates was established based on the cross coupling reaction of an iodobenzene derivative with ZnCuBr(2)CF(2)PO(OEt)(2). The synthetic utility of ZnCuBr(2)CF(2)PO(OEt)(2) was examined to obtain alpha, alpha-difluoromethylenenphosphonates. The method was applied to a synthesis of PNP-inhibitory active compounds by combination of the purine base and alcohols containing difluoromethylenephosphonate. The methodology for the beta-selective N-glycosylation of 2,3-dideoxy glucoside was established by introducing phosphonothioates at the 3-position of glycosyl doners instead of phosphonate. Synthesis of new acylic nucleotide analogues designed based on the structural modification of ARS2267 is also described. Finally, kiral synthesis of some phosphonates was achieved using lipase through kinetic resolution.

The total synthesis of (-)-crispatene

The total synthesis of the molluscan polypropionate (-)-crispatene is described. The synthesis features a palladium-catalyzed cross-coupling to establish a sensitive conjugated tetraene and its Lewis acid-catalyzed cycloisomerization to yield the bicyclo[3.1.0]hexene core of the natural product. The absolute configuration of (-)-crispatene and related molecules is established.

Synthesis and evaluation of multisubstrate analogue inhibitors of purine nucleoside phosphorylases

1,1-Difluoro-2-(tetrahydro-3-furanyl)ethylphosphonic acids (+/-)-cis-4a and (+/-)-trans-4a possessing a (purine-9-yl)methyl functionality at the ring as well as their homologues (+/-)-cis-4b and (+/-)-trans-4b were synthesized and tested as 'multi-substrate analogue' inhibitors for purine nucleoside phosphorylases. Radical cyclization of allylic alpha,alpha-difluorophosphonates 8a,b was applied to construct the alpha,alpha-difluorophosphonate-functionalized oxacycles 9a,b. The IC50 values of the nucleotide analogues (+/-)-cis-4a and (+/-)-cis-4b were 88 and 38 nM, respectively, for human erythrocyte PNP-catalyzed phosphorylation of inosine in the presence of 100mM orthophosphate. The stereochemistry of the inhibitors was found to affect significantly the inhibitory potency. The transisomers (+/-)-trans-4a and (+/-)-trans-4b were ca. 4-fold less potent than the corresponding cis-isomers. At an intracellular concentration of orthophosphate (1 mM), (+/-)-cis-4b, the most potent compound of this series, was shown to have IC50 and Ki values of 8.7 and 3.5 nM, respectively.