J. Org. Chem. 1986,51, 3093-3098 trophotometer, and optical densities were monitored at 250 nm. bo was linear with the slope and A plot of a,b,/AOD vs. a, intercept being equal to l / A c and k d / A t , respectively. The value of Kd was obtained from these linear plots.
+
Identification of Cyclodextrin Complexes. Powder Diffraction of Solid Complexes. X-ray powder photographs of &cyclodextrin, benzoin alkyl ethers, and complexes of cyclodextrin with benzoin alkyl ethers were recorded with a Phillips powder diffractometer employing monochromated Cu K a radiation. Powder patterns of the complexes were different from those of cyclodextrin and benzoin alkyl ethers and therefore it was concluded that microcrystalline complexes have been formed between @-cyclodextrinand benzoin alkyl ether. NMR Studies. Sample Preparation. Solutions of the 1:l complexes were prepared by dissolving 2-3 mg of the complex in about 1mL of DzO. Solutions containing different proportions of guest to host were prepared by stirring 0.5, 1, 2, 3, and 4 mg of the benzoin methyl ether with a solution of 5 mg of @-cyclodextrin in 1 mL of D 2 0 for about an hour. The NMR spectra of all the @-cyclodextrincomplexes and j3-cyclodextrin and benzoin methyl ether in D20 and CDCl, were recorded with a Bruker WH 270 spectrometer equipment with ASPECT 2000 computing system. The difference NOE measurements were made by collecting two sets of free induction decays sequentially in different parts of the computer memory (8K each) corresponding to low power on-resonance saturation of a peak and off-resonance irradiation, respectively. The free
3093
induction decays were recorded by alternating between on-resonance and off-resonance irradiation after each scan, and typically 200 scans were employed. A delay of 3 s between scans and an irradiation period of 3 s were used before acquisition (1.5 s) was started. Identical exponential multiplication was done on both the free induction decays. The difference of their Fourier transforms was then compared with the Fourier transform of the off-resonance irradiated free induction decay to estimate the NOE. No special sample preparation was used for the NOE experiment.
Acknowledgment. Council of Scientific and Industrial Research, Government of India, is thanked for financial support. Registry No. loa, 92549-02-5; lob, 102979-46-4; lOc, 102979-47-5;@-CD/31:l adduct, 102979-42-0;y-CD/3 1:l adduct, 102979-43-1;@-CD/%1:l adduct, 102979-44-2;@-CD/l1:l adduct, 102979-45-3.
Supplementary Material Available: H’ NMR spectra of P-cyclodextrin and @-cyclodextrin-benzoinmethyl ether complex, X-ray powder photographs for (a) 8-cyclodextrin, (b) benzoin isopropyl ether, and (c) inclusion complex of P-cyclodextrin with benzoin isopropyl ether, progress of the reaction with respect to time in the case of cyclodextrin-benzoin methyl ether complex, and Benesi-Hilderbrand plots to estimate Kdfor all three benzoin ethers are given in Figures 1-4, respectively (5 pages). Ordering information is given in any current masthead page.
Facile Synthesis of 2’-Deoxy-3’-keto-and 2’-Deoxypseudouridine Derivatives and Analogues. Palladium(I1)-MediatedCoupling Reactions of Furanoid Glycals Jane Chi-Ya Cheng, Uli Hacksell,’ and G. Doyle Daves, Jr.* Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015 Received January 16, 1986 C-Nucleosides, of either a or @ configuration, are formed selectively in a palladium-mediated coupling reaction acetate. Control of between furanoid glycals and (1,3-dimethyl-2,4-dioxo-1,3-dihydropyrimidin-5-yl)mercuric anomeric configuration is accomplished by suitable choice of substituents for glycal3-0- and 5-0-hydroxy groups; attack of organopalladium reagent and glycosidic bond formation occurs on the least sterically hindered face of the glycal ring. Removal of substituents from the coupled products yielded 2’-deoxy-3’-keto C-nucleosides, which upon metal hydride reduction produced the corresponding 2‘-deoxy C-nucleosides.
In a previous report? we described palladium-mediated coupling of furanoid glycals3 with (1,3-dimethyl-2,4-dioxo-1,3-dihydropyrimidin-5-yl)mercuric acetate ( which formed regio- and stereospecifically a glycosidic carboncarbon bond linking C-5 of the pyrimidine moiety and C-1 of a glycal. This study of C-nucleoside5 synthesis by palladium-mediated coupling of furanoid glycals has now been extended by (a) investigation of the directive effect on organopalladium coupling of various substituents on the glycal oxygens, (b) evaluation of methods for complete (1)Current address: Department of Organic Pharmaceutical Chemistry, Biomedical Center, University of Uppsala, 5-751 23, Uppsala, Swedes. (2) Hacksell, U.; Daves, G.D., Jr. J. Org. Chem. 1983,48, 2870. (3) (a) Cheng, J. C. Y.; Hacksell, U.; Daves, G. D., Jr. J . Org. Chem. 1985,50, 2778. (b) Ireland, R. E.; Thaisrivongs, S.; Vanier, N.; Wilcox,
C. S.J . Org. Chem. 1980,45,48. (4) &ai, I.; Daves, G. D., Jr. J . Org. Chem. 1978, 43, 4110. (5) Hacksell, U.; Daves, G. D., Jr. Prog. Med. Chem. 1985,22,1.
0022-3263/86/1951-3093$01.50/0
or selective removal of C-nucleoside 3’-0 and 5’-0 directive groups, and (c) preparation of 2‘-deoxypseudouridinederivatives by the reduction of corresponding 3‘-keto compounds arising as primary produds of the coupling reaction or following removal of directive groups of product 3’-enols. Directive Effect of Oxygen Substituents on Organopalladium Coupling. The stereochemistry of adduct formation in the organopalladium coupling reaction of furanoid glycals leading to C-nucleosides is exquisitely sensitive to steric factors affecting access to the glycal double b ~ n d . ~ The , ~ , organopalladium ~ reagent (formed by transmetalation of 16!s)attacks the most accessible face (6) Arai, I.; Lee, T. D.; Hanna, R.; Daves, G. D., Jr. Organometallics 1982, I, 742.
(7) Substitution on the double bond does not affect the regiochemistry of the reaction but does depress yields: Lee, T. D.; Daves, G. D., Jr. J. Org. Chem. 1983,48, 399. (8) Kalinoski, H. T.; Hacksell, U.; Barofsky,D. F.; Barofsky, E.; Daves, G. D., Jr. J. Am. Chem. SOC. 1985, 107, 6476.
0 1986 American Chemical Society
3094 J . Org. Chem., Vol. 51, No. 16, 1986
Cheng et al.
of the glycal double bond (however, vida infrag). Thus, each palladium-mediated coupling reaction yields selectively a single palladium adduct of either an a- or a (3-Cnucleoside.2,6In our initial study of furanoid glycals,2we showed that, if both the 3- and 5-hydroxyl groups are substituted with bulky groups, organopalladium reagent attack occurs only from the @ face, whereas, if only the 5-hydroxyl is substituted, attack occurs from the (Y face. In the present study, use of furanoid glycals in which 0 - 3 is substituted and 0-5 is free (2e and 2f) led only to 6-Cnucleosides.
1
20-f
30-1
a: R, R'=CH20CH, b : R:CHZOCH3,
1-Pr ),
c : R, R'=Si(i-Pr)3
d: R:Si(CH,)2t-Eu,
R'=Si(i-Pr)3
e : R d i , R'rCHzOCH, f:
R=H, R'-CH20CH2CH20CH3
The fact that the p-C-nucleosides 3a and 3c form selectively when both the 3- and 5-hydroxyls are identically substituted indicates that the reaction is more sensitive to the steric bulk of the substituent at the allylic (3) position than to that a t position 5 of the furanoid glycal.'O Use of a very bulky group a t 0 - 3 to direct reaction stereochemistry (e.g., triisopropylsilyl) does not depress the yield of coupled product (3b, Table I). Not surprisingly, the presence of such a bulky substituent on the face of the glycal experiencing attack does result in lower, but still quite acceptable, product yields (3c, 3d, Table I). It is noteworthy that, despite its relative lability, the trimethylsilyloxy substituent effectively directs organopalladium adduct formation even though trimethylsilyl is lost during reaction, yielding a 3'-keto C-nucleoside directly (e.g., 2h 812).
coupling of 5-0-substituted glycal2g to form 7 followed by desilylation. It is noteworthy that the intermediate adducts leading to 6 and 7, which possess no syn @-hydrogen or anti P-acetoxy, decompose by syn palladium oxide elimination.'l Removal of Substituents from Carbohydrate Hydroxyls of Product C-Nucleosides. C-Nucleoside products resulting from palladium-mediated coupling of furanoid glycals in which 0-trialkylsilyl groups were used to direct the stereochemistry of adduct formation (i.e., 3c, 3d, 7) react readily with fluoride ion to yield the corresponding 0-unsubstituted a n a l o g u e ~ . ~ J In ~ J 3b ~ where one triisopropylsilyl and one methoxymethyl group were used to differentiate the two carbohydrate hydroxyls, fluoride ion2J2J3selectively removed the silyl group to yield the 5'-O-substituted 3'-keto C-nucleoside 8b. It was
F: HW
5 orF
80 ii-Pr)jSid
MeNN ' Me
-
MeN
-
3b 8b
1
NMe
possible to selectively remove the silyl group from the more labile 3'-O-trialkylsilyl enol ether moieties in the presence of an 5'-0-trialkylsilyl function (3c 8a) by control of the reaction temperature and time. The hope that a tert-bu2h 8C tyldimethylsilyl group could be removed selectively in the presence of a triisopropylsilyl group (see 3d) was not reThe results obtained upon coupling of the 3,5-0-unalized. substituted glycal, 1,4-anhydro-2-deoxy-~-erythro-pentEfforts to remove methoxymethy13and (0-methoxyethl - e n i t 0 1 (4), ~ ~ are particularly informative. This reaction oxy)methyl14 substituents were much less successful owing produced a mixture of the a- and 8-C-nucleosides 5 and to the lability of the C-nucleosides to acid. Attempts to 611in yields of 45% and 29%, respectively (Table I). To remove methoxymethyl groups of C-nucleosides possessing date, this is the only instance in which products resulting unsaturated carbohydrate moieties under acidic condifrom organopalladium attack on both faces of a glycal have tion~ (e.g., ~ ~3a 8b and/or 5) always produced a side been i ~ o l a t e d .This ~ result is indicative that (a) neither product (e.g., 9) in which the carbohydrate ring had opthe hydroxy nor the hydroxymethyl substituent is suffiened. Attempts to remove the (0-methoxyeth0xy)methyl ciently bulky to effectively direct the coupling reaction and group of 3f using zinc bromide14 resulted in migration of (b) the allylic (3) substituent, which is nearer the glycal the (P-methoxyeth0xy)methyl group from the 3'-0 to the double bond, has the greater effect.l0 The a-C-nucleoside 5'-0, forming 8c. 6 was the sole product of a two-step sequence involving Reduction of 3'-Keto C-Nucleosides. A number of 1,3-dimethyl-2'-deoxypseudouridinesand corresponding 3'+-hydroxy isomers were prepared by borohydride re(9) In a related reaction stereochemical mixtures have been observed: Czernecki, S.; Dechavanne, V. Can. J. Chem. 1983,61,533. (10) We have noteda that in coupling reactions of pyranoid glycals the (12) Kraihanzel, C. s.;Poist, J. E.J. Organomet. Chem. 1967,8, 239. organopalladium attack occurs from the face opposite the allylic sub-
-
-
stituent. (11) Hacksell, U.;Daves, G. D., Jr. Organometallics 1983, 2, 772.
(13) Corey, E.J.;Venkateswarlu, A. J. Am. Chem. SOC.1972,94,6190. (14) Corey, E.J.; Gras, J. L.; Ulrich, P.Tetrahedron L e t t . 1976,809.
2’-Deoxy-3’-keto- and 2‘-Deoxypseudouridine Derivatives
R
3a
9
0
0
Met$ANMe
x
Met$ YMe
8c
3f
duction of 3’-keto analogues (8a-c, 5); the results of these reductions are summarized in Table 11. In all cases, the major product possessed a @-3’-hydroxyl; no conditions were found for selective delivery of a hydride to t h e more hindered side of the 3’-carbonyl. It seemed plausible t h a t a metal hydride reagent might chelate to the 5’-oxygen (or other functional group on the carbohydrate /3-face) and deliver a hydride to C-3’.15 This result was not realized, presumably because reaction of t h e hydride reagent with carbonyl is faster than bonding interaction with hydroxyl or other available functionality.
C-Nucleoside Structural Assignments. Product structures were assigned by chemical and spectrometric data contained in Tables I and III. Particularly important in assignment of C-nucleosides to the LY or @ series are the homoallylic coupling constants 4J11,4f (Table I)2Js observed in lH nuclear magnetic resonance (NMR) spectra. When H-1’ and H-4’ a r e trans, 4J1t,4t is >5.0 H z (6 and 7, Table I);2 whereas, when these hydrogens are cis t h e coupling constant is
