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Absolute configuration analog

Compounds analogous to the cobaltammines may be similarly obtained using chelating amines such as ethythenediamine or bipyridyl, and these too have played an important role in stereochemical studies. Thus ct5-[Co(cn)2(NH3)Cl] was resolved into d(+) and /(—) optical i.so-mers by Werner in 1911 thereby demonstrating. to all but the most determined doubters, its octahedral stereochemistry. More recently, the absolute configuration of one of the optical isomers of [Co(en)3] was determined (.sec Panel on p, 1125),... [Pg.1123]

It was found that the signs of rotation of the recovered a-phenylbutyric acid corresponded to the known absolute configurations of the deuteriated alcohols if and only if the size relationships CH3 > CD 3 and H>D were valid. In the case of (-t-)-(S)-2-propanol-l,l,l-d3 (4), the optical yield was between 0-4 and 0 5% (Horeau et al., 1965), corresponding to A AG value of about 23 cal mol at 25°C. For the primary alcohols, quite analogous results were obtained (Horeau and Nouaille, 1966). [Pg.18]

Absolute configurations were ascribed on the basis of an empirical model by analogy to l-hydroxyaUcanephosphonates. They are opposite to those obtained from the NMR spectra of the Mosher s esters of 2-hydroxyalkanephosphonates (entries 4-6) and whose absolute configuration is known. / -Chlorophenyl acetate was used as the acetylating agent. [Pg.176]

Analog ent-(+)-8 is 20-fold more potent than racemic acifran and is threefold more potent than niacin in the cAMP whole-cell assay [55]. The selectivity was also improved with respect to acifran with 10-fold selectivity for GPR109A over GPR109B. The importance of the absolute configuration of ent-(+)-8, which is tentatively assigned S, is demonstrated by the 70-fold better cAMP whole-cell activity of the eutomer compared to that of the distomer. [Pg.79]

Further examination of the extracts of A. cannabina revealed axisonitrile-4 (7), axisothiocyanate-4 (8) and axamide-4 (9) [33], A vinylic isonitrile function was supported by H NMR signals at <51.67 and 1.89, which were assigned to the two isopropylidene methyls of 7. Difficulty in isolating the natural product 9 was circumvented, when isonitrile 7 was transformed to 9, mp 81-84 °C, by acetic acid in anhydrous ether. The absolute configurations of both axanes 1 and 7 and their analogs were later established [31] by studies including X-ray diffraction of the p-bromoaniline derivative of 2 and by CD data of ( + )-10-methyldecalone-l obtained from ozonolysis of the reduction (Na/NH3) product of 1 [1]. [Pg.50]

Epipolasin-B (61), mp 92 °C, was one of two isothiocyanates obtained from the sponge Epipolasis kushimotogensis. Neither the isonitrile nor formamido analog were found with the isothiocyanate. Instead, the thiourea adduct of /J-phenylethylamine was isolated along with another isothiocyanate-thiourea pair [51]. The absolute configuration of 61 was determined by appropriate... [Pg.56]

An independent and virtually simultaneous report by Eabom and coworkers described the preparation of germyl hydride (5), the ethyl analogue of 3, by an analogous route (equation l)3. However, only one of the diastereomeric menthyloxy derivatives (4) could be separated by crystallization the other was not readily purified. Assignment of absolute configuration was not made for 5 but, based on the sign of rotation, it is most likely R. [Pg.196]

The X-ray intensity diffraction data of the given crystal do not allow one to specify which of the two sets describes the actual crystal structure and thus the absolute configuration of the molecule when there is no effect of anomalous X-ray dispersion. Under such conditions Friedel s law holds, which states that the X-ray intensity diffraction pattern of a crystal is centrosymmetric whether the crystal structure is centrosymmetric or not. This does not mean that a false crystal structure containing a center of symmetry is obtained as the solution of the structural problem, but rather that the X-ray analysis cannot differentiate between the two enantiomeric structures. A simple mathematical analogy is provided by the two possible square roots of a number Vj = x. [Pg.5]

The use of a reference axial system, whether right- or left-handed, is completely analogous to the Cahn, Ingold, and Prelog convention (75-77) regarding the specification of the absolute configuration of chiral molecules R and S as depicted in Scheme 11 for molecules with large (L), medium (M), and small... [Pg.39]

This reaction proceeds with retention of configuration since the absolute configuration of the (-l-)-complex has been shown to be by X-ray analysis. Analogously, phosphorus substituted carbonyls react with germanes... [Pg.85]

DHAP-dependent aldolases have also been used as key step in the synthesis of several complex natural products starting from achiral precursors. Thus, the sex pheromone (+)-exo-brevicomin can be synthesized in a multi-step route starting with the stereospecific aldol addition between DHAP and 5-oxohexanal or its 5-dithiane-protected analog catalyzed by FBPA from rabbit muscle ( RAMA ) as the key step by which the absolute configuration of the target is estabUshed (Scheme 4.16) [40]. [Pg.73]

In 1970, Joshi et al. reported the isolation of (—)-isomahanimbine (146), a methyl analog of murrayamine-J (145) from the leaves of M. koenigii. Although, murrayamine-J (145) was isolated from Nature in optically active form ([aJo -6, c 2.1, CHCI3), the absolute configuration is still not known (110). In the same year, Kapil et al. isolated the opposite enantiomer ([a] -1-18.6, c 0.86, CHCI3) from the same source and named it (+)-mahanimbicine (147). The absolute configuration of this alkaloid is also unknown (136). [Pg.55]

In 1996, Wu et al. reported the isolation of murrayamine-M (162), a formyl analog of bicyclomahanimbicine (161) from the leaves of M. euchrestifolia collected in November in Taiwan. The UV spectrum Umax 243, 254 (sh), 292, and 325 nm] of murrayamine-M (162) indicated a 3-formylcarbazole. This assignment was supported by the IR spectrum [Vmax 1605 (aromatic system), 1675 (CHO), and 3300 (NH) cm J. The H-NMR spectrum resembled that of bicyclomahanimbicine (161), but exhibited a formyl group ( 10.08) at C-3 instead of the aromatic methyl group. The deshielded mete-coupled (/=1.7Hz) H-4 at 6 8.48 confirmed the position of the formyl group at C-3. Based on the spectral data, structure 162 was assigned to murrayamine-M (Scheme 2.32). The absolute configuration of 162 is not known (130). [Pg.62]


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See also in sourсe #XX -- [ Pg.1653 ]




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Absolute configuration

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