Stereodivergent Syntheses of Conduramines and Aminocyclitols

Diversification of Simple Arenes into Complex (Amino)cyclitols

Highly oxygenated cyclohexanes, including (amino)cyclitols, are featured in natural products possessing a notable range of biological activities. As such, these building blocks are valuable tools for medicinal chemistry. While de novo synthetic strategies have provided access to select compounds, challenges including stereochemical density and complexity have hindered the development of a general approach to (amino)cyclitol structures. This work reports the use of arenophile chemistry to access dearomatized intermediates which are amenable to diverse downstream transformations. Practical guidelines were developed for the synthesis of natural and non-natural (amino)cyclitols from simple arenes through a series of strategic functionalization events.

Asymmetric Synthesis of Nabscessin A from Inositol and d-Camphor

An enantiomer of nabscessin A (1), an aminocyclitol amide with antimicrobial activity, was synthesized from myo-inositol and dimethyl d-camphor acetal in 14 steps. Formal synthesis of natural nabscessin A was also achieved through the new approach to access both enantiomers of 4,5-di-O-benzyl-myo-inositol, derived from the same set of starting materials. This synthesis features utilizations of the existing framework of myo-inositol and a regioselective esterification.

Stereodivergent routes in organic synthesis: carbohydrates, amino acids, alkaloids and terpenes

The natural occurrence of enantiomers and diastereomers is often encountered.

Ring closing metathesis (RCM) approach to the synthesis of conduramine B-2, ent-conduramine F-2, aminocyclopentitol and trihydroxyazepane

The syntheses of conduramine B-2, ent-conduramine F-2, aminocyclopentitol and trihydroxyazepane were accomplished from a common precursor, through a divergent approach using ring closing metathesis (RCM) as the key step. Tri-O-benzyl-d-glucal was converted to 3,4,6-tri-O-benzyl-1,2-dideoxy-2-iodo-1-p-toluenesulfonamido-α-d-mannose. Exposure to NaBH4 in MeOH resulted in a facile 1,2-transposition of the -NHTs group with concomitant glycosylation to give methyl 3,4,6-tri-O-benzyl-2-deoxy-2-p-toluenesulfonamido-β-d-glucoside, which was converted into methyl 6-deoxy-6-iodo-glucoside in three steps. Zinc-mediated Vasella's rearrangement proceeded smoothly to give the pluripotent formyl-olefin, possessing both electrophilic and nucleophilic sites, which was used as a common precursor in our diversity-oriented approach. Vinylation of the carbonyl group followed by RCM and subsequent deprotection resulted in the successful synthesis of conduramine B-2 and ent-conduramine F-2 for the first time. On the other hand, the Wittig reaction of the formyl-olefin affords the diene that undergoes Grubbs' I catalyzed RCM and deprotection/reduction to provide 3-amino-cyclopentan-1,2-diol. Utilizing the nucleophilic site at the nitrogen of the common precursor, base mediated N-allylation was carried out to obtain the corresponding diene that underwent a smooth RCM to afford trihydroxyazepane.

A chiron approach to aminocytitols by Petasis-Borono-Mannich reaction: formal synthesis of (+)-conduramine E and (-)-conduramine E

A chiron approach to a stereoselective route for the synthesis of aminocytitols from carbohydrates is described. The formal synthesis of (+)-conduramine E and (-)-conduramine E was achieved by utilizing this strategy. The key features of the synthetic strategy include one-pot three-component Petasis-Borono-Mannich reaction to introduce the syn-β-amino alcohol functionality of conduramine E and ring-closing metathesis to construct its carbocyclic core. The present synthetic approach paves the way for stereoselective synthesis of several conduramines starting from carbohydrates.

Regioselectivity in the ring opening of epoxides for the synthesis of aminocyclitols from D-(-)-quinic acid

Efficient syntheses of four aminocyclitols are reported. Each synthesis is accomplished in eight steps starting from D-(−)-quinic acid. The key step involves a highly regioselective ring opening of epoxides by sodium azide.

De novo synthesis of polyhydroxyl aminocyclohexanes

The syntheses of 12 stereochemically diverse polyhydroxyl aminocyclohexane ("aminocyclitols") derivatives are described. These short syntheses require 2-5 steps from N-(2,4-cyclohexadien-1-yl)phthalimide, which is prepared in two steps from tricarbonyl(cyclohexadienyl)iron(1+). The relative stereochemistries of the aminocyclitols were assigned by (1)H NMR spectroscopy as well as X-ray diffraction analysis.

Synthetic applications of chiral unsaturated epoxy alcohols prepared by sharpless asymmetric epoxidation

An overview of the synthesis and applications of chiral 2,3-epoxy alcohols containing unsaturated chains is presented. One of the fundamental synthetic routes to these compounds is Sharpless asymmetric epoxidation, which is reliable, highly chemoselective and enables easy prediction of the product enantioselectivity. Thus, unsaturated epoxy alcohols are readily obtained by selective oxidation of the allylic double bond in the presence of other carbon-carbon double or triple bonds. The wide availability of epoxy alcohols with unsaturated chains, the versatility of the epoxy alcohol functionality (e.g. regio- and stereo-selective ring opening; oxidation; and reduction), and the arsenal of established alkene chemistries, make unsaturated epoxy alcohols powerful starting materials for the synthesis of complex targets such as biologically active molecules. The popularization of ring-closing metathesis has further increased their value, making them excellent precursors to cyclic compounds.

Enantioselective Synthesis of trans-4-Methylpipecolic Acid

An asymmetric synthesis for the preparation of both enantiomers of trans-methylpipecolic acids is described. It is based on Sharpless epoxidation as a chirality source, regioselective ring opening with allylamine, and ring-closing metathesis to construct the piperidine ring. The stereogenic center at C-4 is set by stereoselective hydrogenation that is directed by the alcohol functionality of an intermediate and proceeds with good diastereomeric control (trans/cis 16/1). Crystallization of the Boc-protected amino acid afforded the target products with excellent chemical (98% de) and enantiomeric purity (99% ee).