717. A proton resonance study of the conformations of carbohydrates in solution. Part I. Derivatives of 1,2-O-isopropylidene-α-<scp>D</scp>-xylo-hexofuranose

Proton magnetic resonance spectra of three known diastereoisomers 1,4:3,6-dianhydro-D-glucitol, 1,4:3,6-dianhydro-D-mannitol, 1,4:3,6-dianhydro-L-iditol, and their diacetyl and dimesyl derivatives have been analyzed. The coupling constants obtained have been utilized to determine the conformation of the five-membered rings. Constancy of the couplings between ring protons throughout the series of compounds indicates the existence of one conformation common to all, and this appears to be a composite of the C, and Cz forms. It is significant that intramolecular hydrogen bonding, which occurs in two of the three diastereoisomers, has little or no effect on ring conformation.Canadian Journal of Chemistry, 47, 2395 (1969) It is well known that the hexitols L-iditol, D-glucitol, and D-mannitol readily form 1,4:3,6-dianhydrides under acidic conditions (1). These 1,4:3,6-dianhydrides each have two free hydroxyl groups located at the C-2 and C-5 positions.From inspection of molecular models the 1,4:3,6-dianhydrohexitols have two nearly planar cis-fused five-membered rings in the form of a "V" with the hydroxyl groups at the C-2 and C-5 positions either inside or outside the "V" shaped wedge. As in other ring systems the configuration of a group inside the wedge is designated as endo whereas one outside the wedge is exo. In the L-iditol derivative 1 both hydroxyl groups are exo, in the D-mannitol derivative 3 both are endo, and in the D-glucitol derivative 2 the hydroxyl at C-2 is exo and that at C-5 is endo.The stereochemistry of these compounds has been discussed by Mills (2) and the order of stability of the three compounds as deduced from their ease of formation (3, 4), epimerization (5), and general chemical properties (6, 7) indicates that the presence of an exo substituent increases the stability of the ring to which it is attached, by virtue of the diminished opportunities for interaction between non-bonded substituents. Furthermore the faces of the rings inside the "V" are less accessible than the faces outside, so exo and endo isomers exhibit differences in reactivity in the direction determined by the steric requirements of the reaction in question (8, 9). The extent of intramolecular hydrogen bonding, as determined by infrared spectroscopy in this series of compounds (10) illustrates the influence of structure on such bonding. The C-2 and C-3, and C-4 and C-5 oxygen bonds in the iditol derivative are trans related as in L-threitan so that intramolecular bonding is precluded. A cis relation of the C-4 and C-5 oxygen bonds exists in the D-glucitol analogue permitting a single intramolecular hydrogen bond. In D-mannitol the C-2 and C-3, and C-4 and C-5 oxygen bonds are cis related; two intramolecular hydrogen bonds may occur and the absence of detectable absorption for free hydroxyl groups indicates the completeness of the hydrogen bonding.Correlation of nuclear magnetic resonance Can. J. Chem. Downloaded from www.nrcresearchpress.com by 52.36.4.81 on 05/11/18For personal use only.

Section: Analysis and Discussionmentioning

confidence: 99%

“…coupling constants (J) with dihedral angles (4) is a major step in conformational and configurational analysis. Nuclear magnetic resonance has proved to be an effective means of determining possible conformations of carbohydrate ring systems in solution (11,12). This paper is concerned with the n.m.r.…”

mentioning

confidence: 99%

Conformations of some dianhydrohexitols

Hopton¹,

Thomas²

1969

“…For derivatives 9 to 12, it has not been possible to study if such a dependence existed in the case of oxaphospholane rings, because the 'E form (9,11) as well as the "T5/E5 one (10,12) allow an isoclinal orientation of both the substituents on phosphorus. Thus 9 and 10 (and 11 and 12) cannot be compared with respect to the orientation of the P=O bond, this orientation being the same for the four compounds.…”

Section: Structural Analysis Of Oxaphospholane-ring-containing Derivamentioning

confidence: 99%

Structural analysis of 3-C-phosphonates, -phosphinates, and -phosphine oxides of branched-chain sugars

Neeser¹,

Tronchet²,

Charollais³

1983

A complete nmr study (1H, 13C, 31P) of twelve 3-C-phosphonates, -phosphinates, and -phosphine oxide derivatives of 3-C-branched-chain pento- and hexo-furanoses is reported. For all compounds the configuration at C3 is determined and, for oxaphospholanes 9 to 12, the configuration at the asymmetric phosphorus atom. The 3T2 conformation of the furanose ring of acyclic derivatives 1 to 8 and the conformationally rigid cis-fused oxaphospholane-furanose bicyclic systems of 9 to 12 have been used to study the 3JPCCH vs. θP.H and 3JPCCC vs. θP.C relationships which are specific to this series of compounds. The use of the ν P=O ir stretching frequency, δ 31P chemical shift, and 1JP.C coupling constant values in structural analysis of C-phosphorus-bearing sugars is also reported and discussed.

“…spectrum in chloroform gave a low field doublet with a chemical shift of 4.09 z and a coupling of 4.1 Hz consistent with an assignment of HI for this proton (6). On the basis of this assignment Hz is found at 5.12 z with an Hz to H, coupling of 6.2 Hz.…”

Section: -Isopropylidene-d-hexofur-mentioning

confidence: 64%

Unsaturated derivatives of the 1,2;5,6-di-O-isopropylidene-D-hexofuran-3-uloses

Slessor¹,

Tracey²

1970

The formation of the two 3-0-acetyl-1,2;5,6-di-O-isopropylidene-~-hex-3-enoses from the four 1,2;5,6-di-0-isopropylidene-D-hexofuran-3-uloses is reported. Treatment of the two en01 acetates with hydrogen or deuterium in the presence of palladium or platinum leads to rearrangement as well as reduction and reductive hydrogenolysis of the acetoxy group. This rearrangement makes the en01 acetates unsuitable as intermediates in the stereospecific synthesis of deuterated sugars of high isotopic purity.Canadian Journal of Chemistry, 48,2900 (1970) During our investigation of the reactions and syntheses of the 1,2;5,6-di-0-isopropylidene-Dhexofuranoses (1) it was observed that reduction of the enol acetate of 1,256-di-0-isopropylidenea-D-ribohexofuranos-3-ulose prepared by the method of Meyer zu Reckendorf (2) did not proceed through a simple cis addition of hydrogen. In an attempt to clarify the mechanism by which the reduction proceeds, we have studied the reduction of the en01 acetates derived from diacetone 3-keto-D-ribohexose and 3-keto-Dlyxohexose under a variety of conditions.In the formation of the two en01 acetates from their parent ketones a marked difference in the rate of formation of the final products was observed. Treatment of the four ketones; 1,2;5,6-di-0-isopropylidene-a-D-ribohexofuranos-3-ulose (I), 1,2 ;5,6-di-0-isopropylidene-a-D-xylohexofuranos-3-ulose (2), 1,2;5,6-di-0-isopropylidene-P-D-lyxohexofuranos-3-ulose (3), and 1,2;5,6-di-0-isopropylidene-P-D-arabinohexofuranos-3 -ulose (4) as 1 % solutions of the sugar in 30% acetic anhydride in pyridine at 36" yielded the enolic sugars (5 and 6) (see Scheme 1). A qualitative comparison of reaction rates was provided by following the reactions by thin layer chromatography (t.1.c.) until complete. The results are given in Table 1.An attempt to form 5 by treating the 3-ketodiacetone-D-ribohexose with isopropenyl acetate resulted in the formation of 1,2-0-isopropylidene-3,5-di-0-acetyl-WD-ribohexofuranos-3-use (13) in good yield. The identity of this compound was deduced from nuclear magnetic resonance (n.m.r.), infrared (i.r.), ultraviolet (u.v.), and mass spectroscopy. The n.m.r. spectroscopy indicated the presence of two isopropylidene methyls (8.43 and 8.59 T), two acetate methyls (7.79 z ) , and six non-equivalent protons which were assigned as ?This time may be longer than given. After this length of time breakdown products begin appearing on the 1.l.c. plates.shown in Table 2. The presence of acetate was also confirmed by the presence of an i.r. absorbance at 1750cm-'. The absence of an OH absorbance above 3000 cm-' in the i.r. and the absence of any carbonyl absorption in the 260-340 mp region ruled out the presence of a free or hydrated ketone in 13. The mass spectrum gave a large (M-15)+ peak at m/e 287. Identification of this compound was confirmed by acetylating the known 1,2-0-isopropylidene-a-Dribohexofuranos-3-ulose prepared from 1,2 ;5,6-di-0-isopropylidene-a-D-ribohexofuranos-3-ulose by the method of Theander (3).Reduction of 5 in etha...