Stereoselectivity of Addition of Organometallic Reagents to Pentodialdo-1,4-furanoses: Synthesis of L-Axenose and D-Evermicose from a Common Intermediate
摘要:
The additions of organometallic reagents to two pentodialdo-1,4-furanosides (methyl 3-O-benzyl-2-deoxy-alpha-D-erythro-pentofuranoside and its beta-anomer) were carried out under a variety of experimental conditions. Methylmagnesium halides, methyllithium, methylcerium and the organotitanium reagent MeTi(OiPr)(3) were reacted with the pentodialdo-1,4-furanosides in an effort to determine if the stereoselectivity of addition to the formyl group is the result of chelation or nonchelation control and to determine the effect of anomeric configuration. The stereochemistry of the products was assigned by NMR methods and correlation with known compounds synthesized previously. The stereoselectivity of addition depends on the configuration at the anomeric center of the dialdose, with the beta-anomer giving mainly the product of a non-chelation-controlled addition and the beta-anomer giving the opposite stereoselectivity. The major product obtained from the beta-anomer was utilized as a key intermediate in the synthesis of two branched-chain carbohydrates, axenose and evermicose, found in antibiotics. Methylcerium additions are the most efficient method for introducing the branching methyl group in a 2-deoxyfuranosid-3-ulose.
A new antibiotic, polyketomycin, was isolated from the culture broth of Streptomyces sp. MK277-AF1. The structure was determined by various NMR spectroscopies, X-ray crystallographic analysis and degradation experiments.
Synthesis of Methyl Axenoside and Methyl 3-epi-Axenoside via Ate-Mediated Allylic Substitution (AMAS)
作者:D. McQuade、Brian Ondrusek
DOI:10.1055/s-0033-1339116
日期:——
An ate-mediated allylic substitution (AMAS) of vinylboronates is utilized in the divergent syntheses of the sugars methyl axenoside and methyl 3-epi-axenoside. Other key steps of the synthesis involve the dihydroxylation of the resulting allylic alcohol and selective oxidation of the resultant diol. Benefits of this methodology are also discussed.