Threo configurations

Stmcture-activity and mechanism of action studies indicate that the requirements for chloramphenicol activity are the D-threo-configuration, the... 

Most substrates, with the exception of hydroxypymvate, have a threo configuration of hydroxyl groups at the C-3 and C-4 positions (139). The new stereocenter formed in TK-catalyzed addition is formed in the threo configuration with high diastereo-selectivity (151). Using TK-catalyzed condensations of hydroxypymvic acid with a number of aldehydes a practical preparative synthesis of L-idose [5934-56-5], L-gulose [6027-89-0], 2-deoxy-L-xylohexose, and... 

Ralph, J. Landucci, L. L. Adducts of anthrahydroquinone and anthranol with lignin model quinone methides. 2. Dehydration derivatives. Proof of threo configuration. J. Org. Chem. 1983, 48, 372-376. 

Intramolecular cycloadditions of chiral nitrones provide a useful tool for the preparation of bioactive heterocyclic compounds.63 Shing et al. demonstrated that 1,3-dipolar cycloaddition of nitrones derived from 3-0-allyl-hexoses is dependent only on the relative configuration at C-2,3, as shown in Scheme 8.16. Thus 3-0-allyl-D-glucose and -D-altrose (both with threo-configuration at C-2,3) produce oxepanes selectively, whereas 3-O-allyl-D-allose and -D-man-nose (both with erythro-configuration at C-2,3) give tetrahydropyranes selectively.80... 

Studies202 on the substrate specificity of transketolase suggest that this enzyme will only attack ketoses with the threo configuration at C3 and C4. 

Tetraalkylstannanes with a /i-acyloxy group undergo highly stereospecific elimination to yield Z - or E -unsaturated products, depending on whether the organotin compound has erythro- or threo-configuration, as depicted in reactions 72 and 73, respectively324. 

When a monomeric unit contains more than one tetrahedral stereoisomeric center, the relative configuration of the centers has to be defined. In the case of two adjacent stereoisomeric centers, for instance, -CHA-CHB-, with A B, two configurational signs can be assigned to the bonds connecting the centers (Figure 2.3a). The pairs (+, +) or (—, —) define a relative threo configuration,... 

For the first time, DFT theory has been applied to a study of diastereofacial selectivity in 1,3-dipolar cycloadditions of nitrones to di-3,4-dimethylcyclobutene. ° The stereochemical outcome of the INAC reactions of nitrones (49) and (52) derived from 3-(9-allyl-D-hexoses is dependent only on the relative configuration at C(2,3), and thus 3-(9-allyl-D-glucose (48) and -o-altrose (threo configuration) afford oxepanes (50) selectively whereas 3-O-allyl-D-allose (51) and -D-mannose (erythro configuration) give tetrahydrofurans (53) and (54) selectively (Scheme 18). frani-2-Methylene-... 

This enzyme [EC 1.1.1.16] catalyzes the reaction of galac-titol with NAD to produce o-tagatose and NADH. The enzyme will also catalyze the conversion of other alditols containing an T-threo configuration adjacent to a primary alcohol group. 

For molecules with two stereogenic centers, the traditional descriptors are erythro and threo to which, henceforth, a c (short for carbohydrate) is added for a reason that will become apparent (Table 10). They are unambiguously defined for simple sugars. The backbone is given by the carbon chain the reference conformation is the conformation with all carbon atoms eclipsed. This statement is identical with the requirement of a Fischer projection. If two identical substituents X are located on the same side/opposite sides of the plane traced by the backbone, then the c-erythrojc-threo configuration is assigned. 

The reactive open-chain substrate 29 with the natural D-threo configuration was prepared along a chemoenzymatic route by making use of the common constitutional and stereochemical relationship which substrates of transaldolase share with those of transketolase. Thus, the R-configured 2-hydroxyaldehyde 28 was chain-extended under transketolase catalysis in the presence of 20 as ketol donor to yield the desired aldol. By this approach, several transaldolases could indeed be shown to display different levels of kinetic stereoselectivity. 

The yields of stereoisomeric analogs of 268, compounds having the a-D-threo, (3-L-threo, and a-L-threo configuration, were 74, 66, and... 

Propylene oxide-has two asymmetric carbon atoms, and exists as cis- and trans-isomers. If the polymerization of cis- or trans-propylene oxide- -dj proceeds exclusively by /3-opening and by either retention or inversion of the attacked /3-carbon atom, the polymer composed of the monomeric unit having exclusively an erythro or a threo configuration is expected to be formed. 

Both these enzymes are commercially available and inexpensive. Probably for this reason, they have almost always been utilized in the soluble state, and in great excess. However, it may be observed in Table III that these enzymes are much more efficient when31 immobilized on PAN. Aldolase requires dihydroxyacetone phosphate as ketonic partner, but will accept each of a wide collection of aldehydes as substrates.32 In all cases, the newly built, vicinal diol has the D-threo configuration (see Scheme 6). 

Scheme 6.—The D-threo Configuration of the Newly Built Vicinal Diol in the Reaction Catalyzed by the Glycolysis Aldolase.

In a very recent paper, Seebach and Golinski (59) have proposed a series of rules which explain the preferred formation of the threo-configuration 204 in the condensation of the Michael acceptor 202 with the Michael donor 203. These are ... 

This work and parallel studies by another group5 have been used to assign the threo-configuration to the allylic diol group in the side chain of the frog poison pumiliotoxin B (5). 

As outlined above, MeBmt contains three contiguous asymmetric carbon atoms and an (E)-trans double bond. The MeNH and OH groups are arranged in a threo configuration, whereas the OH and CH3 groups are oriented in the erythro form. 

The vicinal coupling Jl 9 of 3-4-4-3 Hz in the spectra of adlumine [124], hydrastine [125], and narcotine [126] implies a syn clinal relationship between C(l)-H and C(9)-H. Considering conformation consonant with this, together with the chemical shifts of the aromatic protons which are related to the mutual orientation of the two aromatic rings, it is possible to assign the threo-configuration to adlumine and the... 

Starting from D-galactono-1,4-lactone, 2-keto-3-deoxy-D-hexonic acids with either the D-erythro (119) or D-threo configuration (120) were obtained in only three steps.318 Epimerization at C-4 occurred during the base-catalyzed /1-elimination reaction on the galactonolactone derivative 136. 

A vicinal spin-spin coupling constant 7(H1H2) = 2.4 Hz was obtained from the XH NMR spectrum. This value indicates a threo-configuration of 16 that, in turn, supports a... 

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