Samarium diiodide-mediated synthesis of D-3,4,5,6-tetra-O-benzyl-myo-inositol

Desymmetrization of myo-inositol

Chemistry and biology of phosphoinositols have been intensely investigated areas of research over the last 4-5 decades due to their involvement in cellular signal transduction pathways. Efficient laboratory synthesis of enantiomeric derivatives of inositols was a central issue since they were required for the delineation of the myo-inositol cycle as well as for the total synthesis of polyol based natural products and their derivatives. This essentially meant the development of competent methods for the desymmetrization of myo-inositol leading to the preparation of enantiomeric O-substituted derivatives of myo-inositol. This was approached by: the classical resolution methods involving separable diastereomers, the chiral pool synthesis, enzyme catalysis, asymmetric catalysis and preferential crystallization of enantiomers in a racemic conglomerate. This review summarizes results obtained in author's laboratory, as well as those reported in the literature on attempts at desymmetrization of myo-inositol.

Chemical and Biochemical Approaches for the Synthesis of Substituted Dihydroxybutanones and Di- and Tri-Hydroxypentanones

Polyhydroxylated compounds are building blocks for the synthesis of carbohydrates and other natural products. Their synthesis is mainly achieved by different synthetic versions of aldol-coupling reactions, catalyzed either by organocatalysts, enzymes, or metal-organic catalysts. We have investigated the formation of 1,4-substituted 2,3-dihydroxybutan-1-one derivatives from para- and meta-substituted phenylacetaldehydes by three distinctly different strategies. The first involved a direct aldol reaction with hydroxyacetone, dihydroxyacetone, or 2-hydroxyacetophenone, catalyzed by the cinchona derivative cinchonine. The second was reductive cross-coupling with methyl- or phenylglyoxal promoted by SmI₂, resulting in either 5-substituted 3,4-dihydroxypentan-2-ones or 1,4 bis-phenyl-substituted butanones, respectively. Finally, in the third case, aldolase catalysis was employed for synthesis of the corresponding 1,3,4-trihydroxylated pentan-2-one derivatives. The organocatalytic route with cinchonine generated distereomerically enriched syn-products (de = 60-99%), with moderate enantiomeric excesses (ee = 43-56%) but did not produce aldols with either hydroxyacetone or dihydroxyacetone as donor ketones. The SmI₂-promoted reductive cross-coupling generated product mixtures with diastereomeric and enantiomeric ratios close to unity. This route allowed for the production of both 1-methyl- and 1-phenyl-substituted 2,3-dihydroxybutanones at yields between 40-60%. Finally, the biocatalytic approach resulted in enantiopure syn-(3 R,4 S) 1,3,4-trihydroxypentan-2-ones.

Useful access to enantiomerically pure protected inositols from carbohydrates: the aldohexos-5-uloses route

The intramolecular aldol condensation of aldohexos-5-ulose derivatives of the D-xylo and L-ribo stereoseries has been studied. Only one of the four possible inososes was isolated from both stereoseries in reasonable yields (30–38%). The results obtained, together with the previous findings for the L-arabino and L-lyxo stereoseries, allowed for the rationalisation of a mechanism of the reaction based on open-transition-state models and electron-withdrawing inductive effects. Complementary reductions of the intermediate inososes were possible by changing the reaction conditions, and two isomeric inositol derivatives were obtained with complete stereoselection from each inosose. The presented approach permits us to control the configuration of three out of the six stereocentres of the inositol frame and gives access to seven of the nine inositols. Noteworthy, for the D-xylo derivative, the two-step sequence (condensation followed by reduction with NaBH(OAc)₃) represents the biomimetic synthesis of myo-inositol. Furthermore, the sugar-based pathway leads directly to enantiomerically pure selectively protected inositols and does not require any desymmetrisation procedure which is needed when myo-inositol and other achiral precursors are employed as starting materials. As an example of application of the method, the indirect selective protection of secondary inositols’ hydroxy functions, by placing specific protecting groups on the aldohexos-5-ulose precursor has been presented.

Synthesis of allo- and epi-inositol via the NHC-catalyzed carbocyclization of carbohydrate-derived dialdehydes

A synthesis of carbocyclic sugars from carbohydrate-derived dialdehydes using organocatalysis has been developed. Sorbitol, mannitol, and galactitol were converted via 1,6-tritylation, perbenzylation or permethylation, detritylation, and Swern oxidation into 2,3,4,5-tetra-O-alkyl-dialdoses that were cyclized via the benzoin reaction promoted by a triazolium carbene. Manno- and galacto-configured dialdehydes gave predominantly single inosose stereoisomers in up to 75% yield if the mixture was acetylated prior to isolation while the gluco-dialdehyde afforded a mixture of three stereoisomers in 61% overall yield. The inososes were stereospecifically reduced using sodium borohydride and then deprotected to give allo- and epi-inositol in good yield that confirmed the structural and stereochemical assignments.

Synthesis of bishomoinositols and an entry for construction of a substituted 3-oxabicyclo[3.3.1]nonane skeleton

1,3,3a,7a-Tetrahydro-2-benzofuran was used as key compound for the synthesis of various bishomoinositol derivatives. The diene was subjected to an epoxidation reaction for further functionalization of the diene unit. The bisepoxide obtained was submitted to a ring-opening reaction with acid in the presence of water. Various bishomoinositols were synthesized. However, when the reaction was carried out in the presence of acetic anhydride, a substituted 3-oxabicyclo[3.3.1]nonane skeleton was formed. The mechanism of the formation of the products is discussed.

Application of the Quiral Program to the Challenge of Myoinositol Synthesis

The Quiral program helps chemists to choose synthetic approaches to myoinositol or its protected derivatives.

Diastereoselective Synthesis of D- and L-myo-Inositol 3,4,5,6-Tetrakisphosphates from D-Glucose via Dihydroxylation of (+)-Conduritol B Derivatives

Syntheses of D- and L-myo-inositol 3,4,5,6-tetrakisphosphates were achieved via diastereoselective 1,2-addition of vinylcopper reagent with the chiral aldehyde prepared from 1,2,5,6-diisopropylidene-D-glucose, ring-closing metathesis of 1,7-diene with Grubbs catalyst followed by catalytic OsO(4) dihydroxylation of (+)-conduritol B derivatives.

Stereoselective synthesis of myo-inositol via ring-closing metathesis: a building block for glycosylphosphatidylinositol (GPI) anchor synthesis

Here we report a concise stereoselective synthesis of myo-inositol via ring-closing metathesis. A readily available bis-Weinreb amide of D-tartrate served as a key intermediate. [reaction: see text]

Dual enantioselective control in asymmetric synthesis

It is desirable and practical to produce both enantiomers of a target from the same chiral starting material by stereodifferentiation of prochiral compounds, for instance utilizing a chiral ligand derived from a natural (L) amino acid. During the past 7 years, excellent results have been achieved in several cases by multiple stereodifferentiation of chiral ligands derived from (S)-indoline-2-carboxylic acid: highly diastereo- and enantioselective pinacol coupling reactions of chiral alpha-ketoamides gave both (S,S)- and (R,R)-quaternary tartaric acid for the first time; asymmetric Diels-Alder cyclization of chiral acrylamides in the presence of Lewis acid afforded extremely high diastereoselectivities of both opposite configurations of the cyclized diastereomers depending upon the structures of chiral ligands and Lewis acids; and asymmetric alkylation of aldehydes to both enantiomers of secondary alcohols and asymmetric hydrogenation of ketones to both enantiomers of chiral secondary alcohols have been achieved using catalysts derived from (S)-indoline-2-carboxylic acid.

Studies on the SmI2-promoted pinacol-type cyclization: synthesis of the hexahydroazepine ring of balanol

The efficiency of the samarium(II) iodide induced pinacol-type coupling for the construction of seven-membered cyclic amino alcohols has been investigated. With the acyclic carbonylhydrazones 6 and 16, good yields of the hexahydroazepines 22 and 23 were obtained (56-57%) with high trans-selectivity (= 10:1), which compares well with similar reactions generating the corresponding five- and six-membered carbocycles (Fallis, A. G.; Sturino, C. F. J. Am. Chem. Soc. 1994, 116, 7447). It is essential for ring formation that the strongly electron-donating ligand, hexamethylphosphoramide, be present, as in its absense intermolecular pinacol coupling forming the diols 27-30 is the dominant reaction. Hence, the role for HMPA appears not only to increase the rate of electron transfer but also to modulate rate constants for the subsequent reactions (cyclization and pinacol coupling) of the intermediate ketyl. This ring forming reaction has been applied to the construction of the fully functionalized hexahydroazepine ring of the PKC inhibitor, balanol. Initial attempts to develop an asymmetric version of this reaction indicate the use of chiral ligands based on the structure of HMPA.

Synthesis of Trehazolin from D-Glucose

Trehazolin (2) is a specific inhibitor of trehalase, an enzyme that cleaves the reserve carbohydrates of many insects. We describe a short and efficient synthesis of trehazolin (2) and trehazolamine (5) that mimics its hypothetical biosynthesis. Starting molecule for the synthesis of trehazolamine (5) is glucose from which three chiral centers are conserved during the reaction sequence. The remaining two chiral centers of trehazolamine (5) are formed stereoselectively in a reductive cyclization of ketooxime ether 16 and the reduction of oxime ether 18. The overall yield of trehazolamine (5) is 22% over 8 steps from 15. The synthesis of trehazolin (2) from trehazolamine (5) follows a known procedure and is achieved in 63% over 3 steps.