CARBOHYDRATE RESEARCH

ELSEVIER Carbohydrate Research 265 (1994) 237-248

Preparation and crystal and molecular structure of 6-G [ (2s) -2,3-epoxypropyl] -1,2:3,4-di-Q-

isopropylidene-a-D-galactopyranose. Pyranoid ring conformation in 1,2:3,4-di-O-isopropylidene-

galactopyranose and related systems

Peter Kijll a7*, Wolfgang Saak a, Siegfried Pohl a, Bohumil Steiner b, Miroslav Ko& b

a Department of Chemistry, The University, Carl-von-Ussietzky-Str. 9-11, D-24111 Oldenburg, Germany b Institute of Chemistry, Slovak Academy of Sciences, Dtibravskd cesta 9, SK-842 38 Bratislava, Slovak

Republic

Received 22 November 1993; accepted in revised form 9 June 1994

Abstract

The title compound was isolated by several recrystallisations from a 1:l mixture of diastereomers which was obtained in 75% yield from the reaction of 1,2:3,4-di-O-isopropylidene-c~-D-galactopy- ranose with epichlorohydrin. The absolute configuration of this isomer (30% yield) was established by X-ray crystallography. The conformation of the pyranoid ring in this compound is compared to those in related situations. In all these cases the pyranoid ring adopts a heavily distorted conformation which is described on average as between the screw-boat OS, and the twist-boat ( “skew’‘-boat) OT, with deviations in the direction of the boat & in most cases. The puckering parameters for all such reported pyranoid rings were calculated or recalculated, and are given within expanded conventions of carbohydrate nomenclature.

Keywords: Pyranoses; Conformation; X-ray structure; Nomenclature

1. Introduction

1,2:3,4-Di-O-isopropylidene-a+D-galactopyranose is readily available and offers the opportunity for selective derivatisation at the sole unprotected hydroxyl function at O-6.

* Corresponding author.

0008-6215/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SsDIOOO8-6215( 94)00232-O

238 P. iGill et al. / Carbohydrate Research 265 (1994) 237-248

Many such reactions have been described. The aim of the following work was to introduce an epoxypropyl group at O-6 through an ether linkage. Thus, the starting material was treated with l-chloro-2-epoxypropane (epichlorohydrin) under basic conditions to give a 1:1 mixture of diastereomersl, from which one was obtained in a pure state by several recrystallisations. Because it was impossible to deduce the configuration of this isomer 1 in the epoxypropyl part from NMR data, it was subjected to X-ray analysis. This investigation led to a comprehensive reevaluation of the highly distorted conformation of the pyranoid ring in di-U-isopropylidene-galactose derivatives and related structures derived from ara- binose and fructose.

2. Results and discussion

The reaction of 1,2:3,4-di-O-isopropylidene-a+D-galactopyranosein aqueous NaOH with epichlorohydrin in the presence of tetrabutylammonium hydrogen sulfate yields a 1:l mixture of diastereomeric 6-O-epoxypropyl derivatives in 75% yield [ 1 ] _ Another route to a 2’R,S mixture of these diastereomeric epoxides has been reported by starting from the 6- O-ally1 derivative and oxidation with m-chloroperoxybenzoic acid [ 21.

By several recrystallisations of the mixture obtained by the first procedure [l] it was possible to isolate one of the diastereomers in a pure state ( - 30% yield). Because of the obvious difficulties in establishing the configuration of this isomer 1 at C-2’ by NMR methods, suitable crystals were subjected to X-ray analysis.

The relevant crystallographic data for 1 are given in Table 1. The structure was solved by direct methods in the usual way, with the help of the program SHELXTL PLUS (Sie- mens) [ 31. All atoms were refined. The H atoms were introduced at the theoretical positions and treated within a model of riding motion. The final coordinates of C and 0 atoms are listed in Table 2 I. A perspective view (SCHAKAL 92 [4] plot) of a molecule of 1 is presented in Fig. 1, which shows clearly that the structure is as given in the title; the carbon C-2’ is of S configuration.

The pyranose ring in 1 adopts a highly distorted conformation. The puckering parameters according to Cremer and Pople [5] are Q = 61.5 pm, 8= 76.5”, and @= 319.9” [the shape

1 Lists of observed and calculated structure amplitudes, anisotropic thermal parameters, fractional coordinates of hydrogen atoms with isotropic thermal parameters, tables of bond distances and angles, and further information have been deposited with and can be obtained on request from the Director, Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 lEZ, UK.

P. Kiill et al. I Carbohydrate Research 265 (1994) 237-248 239

Table 1 Crystallographic data for 1 a

Formula Mol wt MP ("'3 Crystal dimensions (mm) Space group Cell parameters (pm)

a b c

Volume V ( pm3) Z F(OO0) Calculated density D, (g X cmA3) A WoKa) (pm) CL (cm-l) 28 range (deg) Reflections collected Symmetry independent reflections Observed reflections with I> 4a(I) Number of refined parameters Ratio of valued reflections to parameters Final residual factors (obsd data) R RW

Goodness of fit S Largest difference peak (e X pm-3) Largest difference hole (e X pm -3) Diffractometer

C15H~407

316.35 92-94 1.0x0.3x0.2 m12121

856.6( 1) 1040.9( 1) 1857.5( 1) x656.2(3) X lo6 4 680 I.269 71.073 0.94 3.&50 1714 1693 1183 200 5.9

0.040 0.038 1.31 o.15x106 -0.17x lo6 Siemens STOE AEI D2

a Standard deviations in parentheses.

of the isopropylidene rings is described by puckering parameters Q2 = 29.5 (25.9) pm and ?Z& = 289.2 ( 150.0) “I. Such a distorted conformation seems to be common for all di-O- isopropylidene-galactopyranose derivatives. This situation has been noted already by Kra- jewski et al. [ 61, Boeyens et al. [ 7,8 1, and others. Unfortunately, none of these discussions was comprehensive and there was no agreement as to the exact description of these confor- mations. Therefore, we have calculated or recalculated the puckering parameters according to Cremer and Pople [5] of all the related substances [ 6-301 contained in the current Cambridge Crystallographic Data File. Derivatives of arabinose [ 311 and fructose [ 32- 341 were covered as well, because the L enantiomers are the homologues of the D-@Z&t0 configuration. These calculations were performed by adhering strictly to the rules imposed by Cremer and Pople [ 51; the origin is the ring atom of highest priority, in this case the ring oxygen, and the next atom with the lowest locant (in this case the anomeric carbon C- l) has to follow in a clockwise direction. The results are given in Table 3. All pyranoid rings in these compounds obviously adopt very similar highly distorted conformations which can be described as intermediate between the screw-boat OS, and the twist-boat ( “skew”- boat) OTz with deviations into the direction of the boat Bz, in most of the cases. According to Boeyens [ 35 3, the ideal puckering angles for the former conformation in the cyclohexane

240 P. Kdl et al. / Carbohydrate Research 265 (1994) 237-248

Table 2 Fractional positional parameters a of C and 0 atoms ( X 104) and the equivalent temperature factors U,, b ( X 103) for 1

Atom x Y z UV

o-1 o-2 o-3 o-4 o-5 O-6 o-7 C-l c-2 c-3 c-4 c-s C-6 c-7 c-s c-9 c-10 C-11 c-12 c-13 c-14 c-15

73X2( 3) 8678( 3)

12231(3) 11251(3)

8715( 3) 7933(3) 8432(4) 885X(5) 9823(4)

10833(4) 10137(4)

X594(4) 80X(5) 7381(5) 5928(5) 7591(6)

12667( 4) 13405(6) 13715 (5)

7192(5) 7144( 6) 6946( 6)

4558( 2) 2732( 2) 3604(3) 3417(3) 4729(2) 2443(2)

686(3) 4716(3) 3599(3) 2888(3)

2800(3) 3480(3) 3678(3) 3490(4) 2709(5) 3935(4) 3550(4) 4812(4) 2430(4) 2438(4) 1098(4)

824(5)

1177( 1) 928( 1)

1823( 1) 2941( 1) 2247( 1) 3641( 1) 5009(2) 1495(2) 1192(2) 1733(2) 2496(2) 2560( 2) 3329(2)

703(2)

8W(2) -68(2) 2559(2) 2751(3) 2707(2) 4313(2) 4586(2) 5337(2)

63(l) 45(l) 61(l) 64(l) 45(l) 64(l) 89(l) 45(l) 42(l) 42(l) 39(l) 39(l) 50(l) 51(l) 77(2) 72(2) 51(l)

lOl(2)

63(l) 66(2) 710) W2)

“S ltandard deviations in parentheses. b U,, = l/3 _$ir, ai* a,* a+,,.

Fig. 1. SCHAKAL 92 [41 plot of a molecule of 1, showing atom numbering.

Table 3

P. Kiill et al. / Carbohydrate Research 265 (1994) 237-248 241

Cremer and Pople puckering parameters [5] for derivatives of 1,2:3,4-di-O-isopropylidene-a-D-galactopyranose and of related compounds derived from arabinose and fructose included in the Cambridge Crystallographic Data File of solid-state structures

REFCODE of the Cambridge file/Name a Q (pm) e(O)

ADXPOP/7-Acetamido-6,7,8-trideoxy-1,2:3,4-di-O- isopropylidene-a-D-glycero-D-ga~acto-OCtOpyranose 171 b AXmRG/7-Acetamido-7,8-dideoxy-1,2:3,4-di-O- isopropylidene-P-L-threo-D-galacto-octopyranose hemihydrate [ 81 BANPUB/8-0-Acetyl-1,2:3,4-di-O-isopropylidene-r- glycero-a-D-galacto-octopyranos-7-ulose trimethylene dithioacetal [ 91 BOHXUR/7-Deoxy-1,2:3,4:X,9:11,12-tetra-O-isopro- pylidene-7-nitro-&D-manno-D-glycero-c-D-galacto- dodeco-1,5-pyranos-7-ulo-7,10-furanose [lo] CUTREO/(Z)-7,1l-Anhydro-6-O-benzoyl-8-O-ben- zyl-10-deoxy-1,2:3,4-di-O-isopropylidene-P_L- &no-D-galacto-undec-lo-enopyranos-9-ulose [ (2R,3R) -3-Benzoyloxy-2-( 6-O-benzyl-1,2:3,4-di-O- isopropylidene-D-glycero-~-D-galucto-l,5-pyranos-6- yl) -2,3-dihydro-4H-pyran-4-one] [ 1 l] DABRIH/(Z)-6,10-Anhydro-7-0-benzoyl-9-deoxy- 1,2:3,4-di-O-isopropylidene-P_~-threo-~-galacro-dec- 9-enopyranos-8-ulose [ 121 DIJCII/ (Z)-6,10-Anhydro-7,9-dideoxy-7,9-dimethyl- 1,2:3,4-di-O-isopropylidene-P_~-threo-D-ga~acro-dec- 9-enopyrano&-ulose [ 131 b DITLOHI6-C-( 2-Furyl)-1,2:3,4-di-U-isopropyli- dene-c-D-glycero-D-gaIacro-hexopyranose [ 141 DUMLEC/( 6R)-6-(N-Benzyl-N-hydroxyamino)-6- deoxy-1,2:3,4-di-O-isopropylidene-cY-D-galactopyra- nos-6-ylphosphonic acid dimethyl ester [ 1.51 FAGZUI/1,2:3,4-Di-O-isopropylidene-6-O-tosyl-1~-D- galactopyranose [ 61 FARYOM/l(S)-Acetoxy-3-[6(R)-O-benzyl-1,2:3,4- di-U-isopropylidene-a-D-galactopyranos-&yl]-l- (methyl 2,3,4-tri-O-benzyl-6-deoxy-P_o-galacto- pyranosid-6-yl)prop-2-yne [ 161 ISPGPY/6,6-Dichloro-6-deoxy-1,2:3,4-di-O-isopro- pylidene-5,6-C-methylene-Lu-D-galactopyranose [ 171 JERJULl6-Deoxy-7-C-(2-furyl)-1,2:3,4-di-O-isopro- pylidene-L-glycero-cr-o-galacto-heptopyranose [ 181 JEXLED/&Benzylamino-6-deoxy-1,2:3,4-di-U-iso- propylidene-L-glyceuo_a-D-galacto-heptopyranuronon- itrile [ 191 JUKKEF/3-O-Benzyl-S-C-( 1,2:3,4-di-O-isopropyli- dene-cu-o-galacto-heptopyranos-6-ulos-7-ylidene)-5- deoxy-1,2-U-isopropylidene-cY_D-xylofuranose [ 201

ff-D-GakWOpyranOSe derivatives 64.9 80.8 329.2

64.9 80.6 332.1

molecule I 61.3 molecule II 61.8

molecule I 63.5 molecule II 66.1

60.9

78.6 319.4 81.6 321.0

80.5 325.1 86.1 327.1

75.1 319.2

64.5

59.6

63.2

61.3

62.8

59.2

molecule I 56.2 80.4 324.7 molecule II 58.2 78.3 326.9

63.1 79.7 324.9

63.2 78.2 329.2

64.5 82.0 328.2

79.5

76.7

79.0

77.9

80.3

73.5

329.8

318.2

321.4

323.2

326.5

324.3

242

Table 3 (continued)

P. Kiill et al. / Carbohydrate Research 265 (1994) 237-248

REFCODE of the Cambridge file/Name a Cl (pm) 8 (“) -

@ (“1

JUKKIJ/3-O-Benzyl-6-C-( 1,2:3,4-di-O-iso- propylidene-D-glycer-o-o-gakcto-hexopyr- anos-6-yl)-1,2-O-isopropylidene-D-glycero-fl- L-ido-hexofuranose [ 201 KIDFAE/7-Azido-7-deoxy-1,2:3,4-di-O-isopro- pylidene-P-L-erythro-D-gakrcto-octopyranose [211 KOWGIM/Methyl4,6-O-benzylidene-2-deoxy- 2-C-( 1,2:3,4-di-O-isopropylidene-L-glycero-o-t_- gaEacto-hexopyranos-6-yl)-a-L-cwabino- hexopyranosid-3-ulose monohydrate [ 221 (the values for 8 and @are those of the enantiomer! ) LAI3TIJD/Methyl7-amino-7-deoxy-1,2:3,4-di-O- isopropylidene-D-erythro-cr-D-galacto- octopyranuronate [ 231 SAFZEE/7,7,8,8-Tetradehydro-7,8-dideoxy- 1,2:3,4-di-0-isopropylidene-6-U-methyl-c-D- glycero-D-galucro-octopyranose [ 241 SIYZAB/Methyl Z-(N-acetyl-6-deoxy-1,2:3,4di- U-isopropylidene-a-D-galactopyranos-6-yloxy- amino)-3,6-di-0-benzoyl-2-deoxy-a-o-lyxo-hexo- pyranosid-4-ulose [ 251 SOPDUW/7,8-Dideoxy-1,2:3,4-di-O-isopropyli- dene-cr-D-glycero-D-galacro-act-7-enopyranose E261 SOPFAE/7,8-Dideoxy-1,2:3,4-di-O-isopropyli- dene-P-L-glycero-o-galacto-act-7-enopyranose 1261 TAFJAL/Methyl (Z)-8,9-dideoxy-1,2:3,4:6,7-tri- O-isopropylidene-a-D-rhreo-D-galacto-dec-%eno- pyranuronate [ 271 TAFJEP/Methyl (E)-6-O-benzylL7,8dideoxy- 1,2:3,4-di-O-isopropylidene-a-o-glycero-D-gal- acto-non-7-enopyranuronate [ 27 ] VIDPIHlcis-Dichloro- [ 6-S-(N,N-diethylthiocar- bamoyl)-1,2:3,4-di-0-isopropylidene-6-thio-cr-o- galaetopyranoseJplatinum( II) acetone solvate 1281 VISNUG/6-S-(N,N-Dimethylthiocarbamoyl)- 1,2:3,4-di-0-isopropylidene-6-thio-a-o-galacto- pyranose [ 29] ZMTGOP/7-Azido-8-deoxy-1,2:3,4-di-O-isopro- pylidene-6,7-S-trimethylene-6,7-dithio-c+D-ery- thro-D-guZucto-octopyranose [ 301

64.2

molecule I 65.4 81.0 320.9 molecule II 68.0 79.5 324.9

64.2 81.9 321.1

molecule I 63.6 81.3 333.2 molecule II 62.9 82.0 330.5

molecule I 61.1 76.0 325.8 molecule II 64.9 81.3 327.7

64.5 80.6 324.9

62.6

61.8

59.3

61.3

64.0

62.2

59.4

AVERAGE 62.6 1 61.5 (L-l 61.5

80.2

78.7

75.2

72.5

80.1

80.6

80.1

72.3

328.9

320.2

318.8

313.8

327.4

320.2

324.7

305.2

79.2 (L: 100.8) 324.4 (L: 144.4) 76.5 319.9 103.5 139.9)

KEFSUJf 3,4-0-Isopropylidene-1,2-O-thio- carbonyl-P-D-arabinopyranose [ 3 1 ] c,d

fl-D-Arabinopyranose derivatives c molecule I 58.9 105.0(75.0) molecule II 59.0 103.1(76.9)

144.5t324.5) 140.2t320.2)

P. Kzill et al. / Carbohydrate Research 265 (1994) 237-248 243

Table 3 (continued)

REFCODE of the Cambridge file/Name a Q (pm) 8 (“1 @J(O)

@-D-Fructopyranose derivatives c FOYTA0/2,3:4,5-Di-O-isopropylidene- molecule I 66.2 97.8(82.2) 147.5(327.5) P-D-fructopyranose [ 321 ’ molecule II 65.1 96.4(83.6) 149.0( 329.0) TPHPYR/ (lR)-2-Deoxy-4,5:6,7-di-O-isopro- 64.4 97.4( 82.6) 148.8(32X.8) pylidene-2-methyl-l-C-phenyl-/3-o-arubino-L- glycero-3,4-octodiulo-4,8-pyranose [33] c JERKAS/2,3:4,5-Di-O-isopropylidene-l-O- 63.1 98.9c81.1) 141.6( 321.6) methyl-P-D-fructopyranose [ 341 ’

a Some of the names are not those used by the authors and as such included in the Cambridge Data File; some other names have been corrected to remove inaccuracies. b The reported coordinates describe incorrectly the enantiomer which was not actually investigated. ’ The Band Gvaiues for the L enantiomers, which are homologues of compounds with the D-galacro configuration, are given in parentheses. d This is a derivative with a 1,2- thiocarbonyl instead of an isopropylidene group in this position.

system would be G= 67.5” and @= 330.0”, for the second 8= 90.0” and @= 330.0”, and for the third 8= 90.0” and @= 300.0” [5,35].

Such systematic severe deviations from the usual chair conformations of pyranoid rings are rare. Therefore, not much attention was paid by the carbohydrate community to the development of a common standard of description by accepting these models [5,351. For an ideal chair the puckering parameter 9 is just 0.0” or, inverted, 180.0” and @ has no relevance. To the best of our knowledge afill projection of the Cremer and Pople sphere [ 51 depicting all possible canonical conformations of pyranoid rings, with 8 for latitudes and @ for longitudes (the radius of the sphere given individually by the amplitude of puckering Q), has not been published. Jeffrey and Yates [ 361 gave a map of conformations representing only half of this globe, with the common 4C, conformation ( 8= 0”) in the centre, locating related conformations in such a way (Fig. lb of Ref. 36) that @ angles increase in a counter-clockwise sense. This presentation violates the accepted conventions in carbohydrate chemistry as summarised and depicted by Schwarz [ 371, or as treated by Stoddart [38], and as did Cremer and Pople [5] and Boeyens [35] in the cyclohexane system, because @and the conformations in question should move in a clockwise direction. This situation could explain some of the many confusing statements found in the literature concerning the description of the conformations of distorted pyranoid rings, probably partly due, also, to the fact that the basic explanatory article on cyclohexane conformations of Boeyens [ 351, in adopting and expanding the Cremer and Pople work, appeared in a journal with a very low distribution. Therefore, we give a comprehensive presentation of the full globe for interconversions of the pyranoid ring in Fig_ 2, by adhering to the two-dimensional polar projection of the sphere as was used by Boeyens [35] for the cyclohexane system, with 8 increasing in a clockwise direction, and with 4C, in the centre. This is the region where most carbohydrate conformations have to be located. It is necessary to mention again explicitly that the Cremer and Pople model [ 51 implies highest priority for the ring oxygen with C-l following clockwise under all circumstances, a proposal which is in accord with all accepted rules of nomenclature. This would result logically in renaming the common 4C1 and the inverted ‘C, chair conformations as “C, and 3Co, respectively. Fortunately, as mentioned above, the description of puckering by the Cremer and Pople parameters [5] is

244 P. KdE et al. / Carbohydrate Research 265 (1994) 237-248

P. Kdl et al. / Carhohydratr Re.veurch 265 (1994) 237-248 245

Fig. 2. Polar projection of the sphere of all possible pyranoid ring conformations defined by the puckering parameters 8 and @ as given by Cremer and Pople ]5] for the cyclohexane system, and extended by Boyens 1351, presenting all canonical structures with nomenclative attributes and the sense of involved dihedral angles. The conformations L‘°C3r’ and “3Co” at the poles with 8=0” or 180° are named in accord with all general rules of nomenclature and are equivalent to the conformations traditionally described in the carbohydrate literature as %Z, and ‘C,, respectively. The twist-boat conformations Tat the equator are identical to those desribed as “S” (“skew’‘-boat) in carbohydrate nomenclature [ 37,381, whereas the screw-boat conformation S is another canon- ical conformation not covered until now by carbohydrate nomenclature. Representative samples of all canonical conformations are depicted, with atoms in reference planes dotted. The location of 1 on the sphere with radius Q z=- 0 of the infinite numbers of conformers is given.

not essential for pyranoid rings in more or less ideal chair conformations. However, in those cases in which distortions are observed (for which the amplitude of puckering Q is a measure), six different ideal canonical conformations, the chair included, should be con- sidered [35] (compare Fig. 2), with the infinite number of intermediate conformations located somewhere between these (the all planar conformation P, with Q = 0, is a singular- ity) : Chair (C) with 8= 0” or 180” (inverted C) 8 = 0 at the poles Half-chair (H) with 8= 50.8” or 129.2” (inverted H) (tan 8 = + fi) and @=nX60”+30” Envelope (E) with 8= 54.7” or 125.3” (inverted E) (tan @= + fi) and @= PE X 60” Screw-boat (S) with 8= 67.5” or 112.5” (inverted S) [tan 0 = f ( 1 + fi) ] and ~=nX60”+30” Boat (B) with 8= 90.0” and @= n X 60” at the equator Twist-boat ( T) with 8 = 90.0” and @= y1 x 60” + 30” at the equator (n=O, 1, 2, 3, 4, 5)

It is very important to mention that the twist-boat (T) is identical with the twist-boat/ skew-boat ’ ‘S” as defined by carbohydrate nomenclature [ 37,381. However, the designation S stands for a different, intermediate, canonical conformation, namely the screw-boat [ 351, which was not considered in the basic articles [ 37,381 on the nomenclature of conformations of the pyranoid ring. Therefore, the letter “S” in the Schwarz and other cycles [ 37,381 has to be changed to “7”’ without altering the descriptors (compare Fig. 2). The difference between the screw-boat S and the twist-boat T ( “skew” “ S’ ’ in carbohydrate nomenclature) can be summarised as follows:

In the twist-boat T ( “skew-boat”), a plane is made up of three adjacent ring atoms which are joined by a fourth atom separated on both sides by two other atoms situated on opposite sides of this plane. A representation of this conformation (compare Fig. 2) resembles that used for the twist conformation T of furanoid rings. Therefore, it should be no problem for carbohydrate chemists to accept the designation T also for the related pyranoid case. Simi- larly, it is proposed to take the letter E as the symbo1 for the pyranoid L ‘sofa”/“half-boat” conformation and the description ‘ ‘envelope’ ’ because of its relationship to the furanoid envelope conformation.

The screw-boat S establishes two planes made up of four atoms in the 1,3 position: “The two planes have two atoms in common, and between the two atoms, diagonally across from them, is a dislocation - hence the name screw-boat. The atom at the top of the dislocation is set as a superscript and the lower one as a subscript” [35]. In the OS1 conformation depicted in Fig. 2, atoms 1,2,3,4 and 3,4,5,0 make up these planes, for instance.

246 P. Kiili et al. / Carbohydrate Research 265 (1994) 237-248

AI1 the conformations given in Fig. 2 are chiral and are mirrored through the centre of the sphere into the respective enantiomers. A change of the absolute configuration, which resembles a ring inversion, therefore transforms 8 into 180” - 8 and @ into 180” + @. The respective puckering parameters of ~-1 would thus be O= 103.5” and @= 139.9” with the resulting description of the conformation as intermediate between 5So and *To with devia- tions in the direction of *y5 B. This is the region where all the derivatives of D-arabino and D-$-Z&O configuration mentioned in Table 3 are located.

The isopropylidene rings also adopt distinct and very similar conformations in all these compounds. They are less relevant, and the data are not given here.

The conformations as observed in the solid state are also preponderant in solution. The reported NMR data for the title compound 1 (see below) are, in this regard typical, and differ only very slightly from those of the parent 6-hydroxy compound, whose data were also recorded at 500 MHz for purposes of comparison, but are not given.

3. Experimental

General me&&.-The ‘H and 13C NMR spectra were recorded on Bruker AM-300 and AMXR-500 spectrometers for CDCl, solutions with Me,Si as an internal standard. For the assignment of signals in the 13C NMR spectrum, DEPT and semiselective INEPT techniques were used. IR spectra were recorded on a Perkin-Elmer G-983 instrument. EI mass spectra (70 eV) were measured on a Finnigan Mat SSQ 710 spectrometer. The conditions of the X-ray structure analysis are given in Table 1 (temperature of measurement 296 K) . Puck- ering parameters according to Cremer and Pople [ 51 were calculated within the respective options of the PLATQN program [ 39 ] .

Preparation of the Me compound l.-To a vigorously stirred mixture of aq 50% (w/ w) NaOH (13.3 mL), epichlorohydrin (8.3 mL, 0.11 mol), and tetrabutylammonium hydrogen sulfate (0.28 g) was added 1,2:3,4-di-@isopropylidene-cY-D-galactopyranose (5.2 g, 0.02 mol) gradually during 30 min under cooling by ice, keeping the temperature below 28°C. After 4 h, the mixture was poured into ice-water (50 mL) and the aqueous phase extracted with ether (3 x 100 mL). The ethereal extract was washed with brine to neutrality, dried over Na,SO,, and filtered. After evaporation of the solvent, the residue was chromatographed on a column of neutral alumina using 3:2 EtOAc-hexane as eluent, yielding 4.7 g (75%) of the product (Rf 0.88) ; mp 6S-79°C. After four crystallisations from ether and recrystallisation from heptane, 2.2 g (32%) of the pure S-diastereomer 1 were obtained; mp 92-94°C; [ LY]~ - 60.4” (c 1, MeOH). NMR data: ‘H (500 MHz), 6 1.332, 1.337, 1.443, 1.545 (4 s, each 3 H, 2XCMe,), 2.604 (dd, 1 H, J3,a,3fb -5.0, JZv,3Pb 2.7 HZ, H_3’b), 2.785 (dd, 1 H, J2J,3ja 4.3 Hz, H-3/a), 3.166 (ddd, 1 H, Jlna,*, 3.2, Jl,b,2v 5.8 Hz, H-2’), 3.448 (dd, 1 H, Jl,a,l,b -11.6 Hz, H-l’b), 3.640 (dd, 1 H, J6a,6b -10.3, Js,6b 6.9 Hz, H-6b), 3.745 (dd, 1 H, J5,6a 5.3 Hz, H-6a), 3.808 (dd, 1 H, H-l’a), 3.991 (ddd, 1 H, JG,s 1.9 Hz, H-5), 4.249 (dd, 1 H, J3,4 7.9 Hz, H-4), 4.306 (dd, 1 H, J,,z 5.0, J2,3 2.4 Hz, H-2), 4.598 (dd, 1 H, H-3), 5.534 (d, 1 H, H-l); 13C (125.8 MHz), 6 24.5, 24.9, 26.0, 26.1 (2XCMe2),44.4 (C-3’), 50.8 (C-2’), 67.1 (C-5), 70.3 (C-3), 70.6 (C-2), 70.7 (C- 61, 71.2 (C-4), 72.3 (C-l’), 96.4 (C-l), 108.6 and 109.3 (2XCMe,). IR (KBr pellet):

P. IGIl et al. / Carbohydrate Research 265 (1994) 237-248 247

1090 (CH&--CH,), 851 cm-’ (oxirane). Mass spectrum: m/z (I,) 301 (lOO%, G’-CH,), 243 (7%), 229 (lo%), 171(13%).

Acknowledgements

The help of Privatdozent Dr. J. Kopf (University of Hamburg) and Dipl. Chem. M. Bischoff (University of Oldenburg) in retrieving the Cambridge Crystallographic Data File is appreciated. Dipl. Ing. D. Haase (University of Oldenburg) provided valuable assistance in the X-ray calculations. The referees are thanked for valuable advice and help.

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