Hydroxylations stereochemistry

The 10,11-epoxide of chlorovulone I (107) was also obtained in low yield (0.05%) from the hexane extract of C. viridis [124], Its structure was assembled from spectroscopic data which showed a high degree of similarity to that obtained for chlorovulone I (100) except for UV and 1H NMR features due to the Cl0,11-olefin. Confirmation of structure came from synthesis of 107 by epoxidation of chlorovulone I. Epoxy-chlorovulone I (107) was found to possess the same 12R hydroxyl stereochemistry. The cis relationship of the epoxide and hydroxyl group was indicated by an intramolecular hydrogen bond as revealed by characteristic IR absorptions at high dilution. This 10,11-epoxide derivative... 

Liu Y, Reineke TM (2005) Hydroxyl stereochemistry and amine number within poly(gly-coamidoamine)s affect intracellular DNA delivery. J Am Chem Soc 127(9) 3004-3015... 

Figure 27 Altering chain extension by DEBS 1 +module 3+TE. (a) DEBS 1 +module 3+TE makes two products in vivo, (b) KRS from DEBS was introduced in place of KR2. The resultant hybrid PKS produced the expected tetraketide products, (c) The KR domains from RAPS modules 2 and 4 were introduced in place of DEBS KR2. The resultant hybrid PKSs both produced a triketide lactone product incorporating novel (R)-hydroxyl stereochemistry at C-3.

It is the second feature of the Newton-Roberts approach that is valuable from a stereocontrol point of view. In the Corey lactone approach, the synthon itself already contains C-13 of the co-sidechain, which enforces the use of a reagent containing a C-15 carbonyl, making control of the C-15 hydroxyl stereochemistry difficult, whereas in the tricycloheptanone approach the entire sidechain (C-13 to C-20) is added in one piece, which means that this sidechain can be readily introduced in the form of a reagent that has this sidechain stereochemistry already in place. Following the addition of the co-sidechain and a Baeyer-Villiger oxidation to the lactone, the later steps to add the a-chain are essentially identical to the Corey lactone route because the lactones are regioiso-meric. 

Treatment of the laterally lithiated amide generated from lactam 273 with LDA with /ra r-2-phenylsulfonyl-3-phenyloxaziridine 33 afforded hydroxyl product 274 in 85% yield as a single isomer <1999JOC8627>. Use of (+)-(camphorsulfonyl)oxaziridine 202 gave similar results. The /ra t-stereoselectivity is consistent with the earlier finding that the hydroxylation stereochemistry is controlled by nonbonded steric interactions in the transition state such that the oxygen of the oxaziridine is delivered from the sterically least hindered direction. Treatment of 275 with LDA followed by (+)-(camphorsulfonyl)oxaziridine 202 afforded hydroxyl product 276 in 47% yield and 60% ee <1997T8881>. 

The stereochemistry of the enediols and enediolates involved in non-enzymic sugar isomerisations is unknown, but protein X-ray crystallography, particularly of isomerases in complexes with stable analogues of the enediolates, has established the hydroxyl stereochemistry to be cis. The argument from Natural... 

Krauser JA, Guengerich FP (2005) Cytochrome P450 3A4-catalyzed testosterone 6fl-hydroxylation stereochemistry, kinetic deuterium isotope effects, and rate-limiting steps. J Biol Chem 280 19496 10506... 

Generating Haworth formulas to show stereochemistry m furanose forms of higher aldoses is slightly more complicated and requires an additional operation Furanose forms of D ribose are frequently encountered building blocks m biologically important organic molecules They result from hemiacetal formation between the aldehyde group and the C 4 hydroxyl... 

The free anomeric hydroxyl group IS the one shown at the far right of the preced ing structural formula The symbol is used to represent a bond of variable stereochemistry... 

In the olivanic acid series of carbapenems the ( )-acetamidoethenyl grouping can be isomerised to the (Z)-isomer (19) (22) and reaction with hypobromous acid provides a bromohydrin that fragments to give a thiol of type (20) when R = H, SO H, or COCH. The thiol is not isolated but can react to provide new alkyl or alkenyl C-2 substituents (28). In the case of the nonsulfated olivanic acids, inversion of the stereochemistry at the 8(3)-hydroxyl group by way of a Mitsunobu reaction affords an entry to the 8(R)-thienamycin series (29). An alternative method for introducing new sulfur substituents makes use of a displacement reaction of a carbapenem (3)-oxide with a thiol (30). Microbial deacylation of the acylamino group in PS-5 (5) has... 

Neomethymycin (12, R = H, R = OH), an isomer co-produced with methymycin, is the product of hydroxylation at C-12 rather than C-10 of the lactone (34,35). The corresponding aglycone, neomethynoHde (13, R = H, R = OH), was isolated with methynolide from broths of S. vene elae (36). The stereochemistry of 12(R)- for neomethynoHde was estabHshed by total synthesis (37). YC-17 (12, R = R = H), also found in broths of S. vene elae is a possible precursor of methymycin and neomethymycin. The hydroxyl groups at C-12 and C-10 are probably added as late steps in the biosynthesis (38). 

The stereochemistry of epoxidation of 5j5-steroids is changed from to predominantly a by the presence of an a-oriented hydroxyl group. The magnitude of this hydroxyl effect is less in polar solvents, as shown by the... 

A 17a-methyl in the product of ring D homo-annulation of 17-hydroxy-20-keto steroids may limit the general synthetic utility of the reaction. On the other hand, the 17a-hydroxyl group gives additional flexibility in planning further transformations. Moreover, by adjusting reaction conditions, the stereochemistry of the products can be changed. 

The first objective was the conversion of L-tryptophan into a derivative that could be converted to pyrroloindoline 3, possessing a cis ring fusion and a syn relationship of the carboxyl and hydroxyl groups. This was achieved by the conversions shown in Scheme 1. A critical step was e. Of many variants tried, the use of the trityl group on the NH2 of tryptophan and the t-butyl group on the carboxyl resulted in stereospecific oxidative cyclization to afford 3 of the desired cis-syn stereochemistry in good yield. 

Hydroxylation of ris-2-butene with 0s04 yields a different product than hydroxylation of tram-2-butene. Draw the structure, show the stereochemistry of each product, and explain the difference between them. 

Hydroxylation of c/.v-2-butene with OsO yields 2.3-butanedio]. What stereochemistry do you expect for the product (Review Section 7.8.)... 

Diols can be prepared either by direct hydroxylation of an alkene with 0s04 followed by reduction with NaHSOj or by acid-catalyzed hydrolysis of an epoxide (Section 7.8). The 0s04 reaction occurs with syn stereochemistry to give a cis diol, and epoxide opening occurs with anti stereochemistry to give a trans diol. 

Desilylation of 20, followed by oxidation of the secondary hydroxyl group furnishes racemic 1 in a yield of 81 %. Spectroscopic and bioassay characteristics of synthetic ( )-1 matched natural peripla-none B in every detail. The constitution and relative stereochemistry of the elusive American cockroach sex excitant periplanone B (1) has been secured in a very elegant way.5... 

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