Branched-chain sugar nucleosides. IV. 9-(3-Deoxy-3-C-"hydroxymethyl"- p(and a)-D-allofuranosyl and ribofuranosy1)adenine

ALEX ROSENTHAL AND MATEJ SPRINZL Departme~t of Cl~emistry, University of British Columbia, Vatzcouver, British Colutnbia

Received June 25, 1969

Hydroboration followed by alkaline hydrogen peroxide oxidation of 1,2:5,6-di-0-isopropylidene-3-C- methylene-a-D-ribo-hexofuranose (2) yielded 3-deoxy-3-C-"hydroxymethyl"-l,2:5,6-di-O-isopropylidene- a-D-allofuranose (3) and partially hydrolyzed 3 in a total yield of 88%. Compound 3 was hydrolyzed selectively to the 1,2-monoisopropylidene derivative 5, which was converted via benzoylation followed by acetolysis into the 1,Zdiacetate 7. Condensation of the latter compound with chloromercuri-N- benzoyladenine in the presence of titanium tetrachloride, followed by deblocking with methanolic sodiitm methoxide, yielded 9-(3-deoxy-3-C-"hydroxymethyl"-8(and a)-D-allofuranosy1)adenine in yields of 44 and 4% respectively, based on 7. The over-all yield of 10 based on 3 is 20%. Sodium rneta- periodate oxidation of 10, followed by sodium borohydride reduction of the alrle/~ydo-derivative, afforded 9-(3-deoxy-3-C-"hydroxymethyl~-~-ribofuranosy)adenine (11) in 81 % yield.

Direct acetolysis of 3, followed by conversion of the mixture of peracetates into a mixture of glycosyl chlorides, and finally condensation of the latter with 8 gave the blocked crystalline 0-D-nucleoside 9 in an over-all yield of about 9%, based on 3. Subsequent unblocking of 9 gave a nucleoside having the same physical constants as 10.

Canadian Journal of Chemistry, 47, 4477 (1969)

In continuation of our studies on the synthesis of branched-chain sugar nucleosides (1-3) we now wish to reDort the svnthesis of two nucleo- sides having a'hydroxy&ethyl group on C-3 of the furanosyl ring. The starting material for this research was 1,2:5,6-di-0-isopropylidene-a-D- ribo-hexofuranos-3-ulose (1) which was con- verted into the branched-chain unsaturated sugar 1,2:5,6-di-0-isopropylidene-3-C-methyl- ene-a-D-ribofuranose (2) by application of a Wittig reaction to 1 (3). I t was envisaged that hydroboration of the methylene group on C-3 of 2 might give the desired product. Previous workers (4, 5) have reported the application of the hydroboration reaction (6) to carbohydrates containing either a terminal or endocyclic double bond to yield hydration products in low yield. Both in the general field and in the few carbohydrates investigated hydroboration was found to proceed in ail anti-Markownikov manner. When the hydroboration reaction (4, 5 ) was first applied to 2 using a stoichiometric amount of diborane then only a negligible yield of the diborane-unsaturated sugar adduct was formed. However, when a very large excess of diborane was allowed to react with 2 followed by an immediate alkaline hydrogen peroxide oxida- tion of the adduct, then two compounds 3 and 4 in the ratio of 3:l were formed in 88% yield. These substances were separated by column chromatography. Compounds 3 and 4 showed

identical H-2 resonances (triplet) thus confirming that each was formed via hydroboration. Be- cause of the much slower thin-layer chromatog- raphy (t.1.c.) mobility of 4 than that of 3 it was reasoned that a partial hydrolysis of 3 might have occurred during the reaction or work-up of 3. This postulation was confirmed by carrying out a selective hydrolysis of 3 and 4 to afford an identical substance 5 from each. The structure of 3 was readily ascertained from its proton magnetic resonance (p.m.r.) spectrum. As already indi- cated above the H-2 signal of 3 appears as a triplet (two overlapping doublets) at r 5.28 showing that H-2 is coupled to H-3 and to H-1. Because H-2 of the glucofuranose derivatives (in which H-3 is trans to H-2) gives a doublet (no measurable or less than 0.7 Hz coupling between H-2 and H-3) (7), it was inferred that H-2 and H-3 of 3 must be in a cis orientation. This is supported by the fact that the H-2 signal of 1 ,2:5,6-di-0-isopropylidene-a-D-allofuranose is a triplet. Therefore, 3 is undoubtedly 3-deoxy-3- C-"hydroxymethy1"- 1,2 :5,6-di-0-isopropylidene- a-D-allofuranose. Compound 3 was readily converted into its crystalline p-bromobenzene- sulfonate derivative.

Benzoylation of 5 in the usual way afforded 1', 5 ,6 - t r i -0 - benzoyl-3-deoxy-3-C-"hydroxy- methyl"- 1 ,2-0-isopropylidene-r-D-allofuranose (6) in 88% yield. Acetolysis of the latter with acetic anhydride - acetic acid - sulfuric acid gave

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4478 CANADIAN JOURNAL OF CHEMISTRY. VOL. 47, 1969

NHBz

(1) 104- NaOCH t--- HO-ca 3 (2) NaBHj CH30H BzO-cK$

the anomeric mixture of diacetates 7 in 65% mixture of the P-D (and a-D)-nucleosides 10 in yield. Condensation of 7 with 6-benzamido- the ratio of 11 : I . Fractional crystallization of chloromerc~~ripurine (8) by the titanium tetra- this mixture from 80 % methanol-water afforded chloride method (1) gave a mixture of blocked crystalline 9-(3-deoxy-3-C-"hydroxymethyl"-P- nucleosides 9 which was immediately unblocked D-allof~~ranosyl)adenine (10) in 44% yield, based with rnethanolic sodium methoxide to give a on the diacetate 7. After the solvent from the

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ROSENTHAL A N D SPRINZL: BRANCHED-CHAIN SUGAR NUCLEOSIDES. I V 4479

mother liquor was evaporated to dryness, the residue was partially separated by gradient elution cliro~iiatograpliy on Dowex 1 x 2 (OH-) resin ( 5 ) using water, followed by aclueous methanol as developers, to afford pure P-D- anomer and a mixture of the a-D- and P-D- anomers (10). The latter was separated by preparative paper chromatography to yield the syrupy c ~ - ~ - a n o ~ i i e r of 10 in about 4 % yield.

The assignment of structure of both anomers of 10 was based on ultraviolet (u.v.), optical rotatory dispersion (o.r.d.), and p.1ii.r. spectra. Such evidence, although not u~lequivocal when only one anoiiier is available, as in our first investigation (I), is more definitive for the proof of structure of both anorners 10 because a comparison of tlie physical measurements of both could be made. For example, as expected, 10a gave a positive Cotton effect whereas 10 showed the normal negative Cotton effect. From a niechanistic viewpoint, it is surprising that branched-cham sugars having either a hydroxy- ethyl or methyl group on C-3 gave only the p-D-anomeric nucleoside (1, 3) whereas the hydroxynietliyl analogue reported herein afforded both anomers.

I n order to prepare the ribo nucleoside 11, the p-D-allo-n~~cleoside (10) was degraded by sodiuni metaperiodate to the nlcleliyc/o nucleoside. The latter was immediately reduced with sodium borohydride to yield crystalline 9-(3-deoxy-3-C- "l~ydroxymethyl"-P-D-ribofuranosyl)adeiine (1 1) in 81 0/;: yield. I11 the latter nucleoside, nuclear magnetic resonance (n.1ii.r.) evidence (H-1 gave a doublet having J, ,2 = 2 Hz) substa~itiates the p-anomeric configuration of 11 and of 10.

In an attempt to increase tlie over-all yield of 10 from 3, the latter was subjected to fewer steps as outliiied below. Acetolysis of 3 followed by treatment of the resulting n i ix t~~re of peracetates with anhydrous hydrogen chloride in ether gave a mixture of glyco~yl halides. This mixture was not p~~rified but was condensed with 8 to afford a mixture of compounds. The main fluorescing component of this mixture was separated by preparative t.1.c. on silica gel to yield a crystalline blocked nucleoside in an overall yield of about 9 which was deblocked with metlianolic sodium methoxide affording a non-crystalline nucleoside having the same R, and L I . ~ . spectrum as that of an authentic sample of 10. The low yield of 9 might be ascribed to the fact that acetolysis

of 3 probably yielded both the allopyranose and allofuranose peracetates because of ring opening d ~ ~ r i n g the reaction (t.1.c. ofthe peracetate mixture showed at least three components and n.m.r. revealed three low field signals that niight be attributed to three anomeric hydrogens of three different peracetates); the allofi~ranose per- acetates on treatment with hydrogen chloride would be converted into a mixture of allo- furanosyl chlorides but the a-allopyranose peracetate would be unaffected since it is known that only the P-pyranose peracetate reacts with anhydrous hydrogen chloride in ether.

I n an attempt to shed additional light on the chemistry of branched-chain sugars, the blocked branched-chain sugar 3 was unblocked by two different routes. In tlie first method, when 3 or 7 was subjected to acetolysis followed by treatment with niethanolic s o d i ~ ~ m metlioxide, a mixture of four distinct compounds (as evidenced by paper chromatography) was formed. When the major component having the highest R, was separated by preparative chroniatography aiid allowed to stand in water, it surprisingly gave a co~nplex mixture of substances which could not be separated. In the second procedure 3 was hydrolyzed with dilute acid to i v e a niixture of three substances, two of which only liad the same R, as those obtained by acetolysis and saponifi- cation of 3.

Experimental General considerations were similar to those previously

described (I , 3). Silica gel G was ~ lsed in the t.1.c. For column chron1atography Silica gel Woelm 100-200 mesh, activity grade 11, was used.

HyrlroDorotiott Follolr~erl hy Alliolitte fTyc/rogetz Peroxide Oxirlcrtiort of /,2:5,6- Di-O-isopro/)j,lirIet~e-3-C- t t z e ~ l t y l e ~ ~ e - r - ~ - ~ i b o - I ~ ~ . ~ o f i i r r ~ t t o . e ( 2 ) to Yielrl 3- Deoxy-3-C-"lzyrIroav~~tt~et/~yl"- I,Z:5,6-rli-0- i .o / ro / / i~ /e le -r -D-o110f i1ro .e (3)

Into a solution of compound 2 (3) (I .3 g, 0.005 mole) in anhydrous tetrahydrofuran (16nil) was slowly bubbled a large excess of commercial diboranc for 4 11 at room tempcra t~~re . It is essential that tlie tetraliydro- furan be s a t ~ ~ r a t e d with diborane. In 111.eliminary experi- nients a stoicliiometric amount of diboranc gave a negli- gible yicld of product in which diborane had added to the olefinic d o ~ ~ b l e bond of the silgar. After tlie reaction niixture was cooled to 0' a 50% aqueous mixture of tctrahydrofuran (5 ml) was added dropwise with v i g o r o ~ ~ s stirring, followed by the addition of 2 N s o d i ~ ~ n i hydroxide (15 nil) and then 30% hydrogen peroxide (8 nil). T h e reaction mixture was allowed to come to room tempera- ture and stirred for a further 0.5 11. After the solvent was ren~oved ~Lnder reduced pressure. the residue was

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4480 CANADIAN JOURNAL OF CHEMISTRY. VOL. 47, 1969

dissolved in 40 mI water and the aqueous solution extracted with 4 x 20 ml of ether. The combincd ether extracts were dried over magnesium sulfate, filtered, and evaporated under reduced pressure to afford 1.23 g (88 %) of a syrup. An aliquot of this product was separated by preparative t.1.c. on silica gel G using a I : I mixture of benzene-ethyl acetate as developer into two com- ponents having Rfls of 0.5 and 0.2 in the ratio of 3:l. The faster moving component (3) was a syrup, [a],22 + 103" (c 2, chloroform), r(CDC13), 4.25 (d, J1,z = 4 Hz, H-1), 5.28 (t, H-2), 6.1 (m), 6.95 (peak due to H of OH), 7.9 (nl, H-3), 8.6 (two isopropylidene groups). The slower moving fraction 4 had + 96' (C 1, chloroform) and r(CDC13) 4.25 (d, J,,, = 4 Hz, H-1), 5.28 (t, H-2), 6.25 (m), 6.95 (s, duc to OH), 7.9 (m, H-3), 8.4-8.9 (two isopropylidene groups). Selective hydrolysis (1) of 3 and of 4 using 0.1 N sulfuric acid yielded the same compound 5, described in a subsequent section.

I-O-p-Brorr1ophetryls11,fonyl-3-deoxy-3-C- "/1yc~roxymethyl"-1,2:5,6-di-O-isopropy~ideerre-a-~- allofrr~rrose (30)

An amount (0.137 g) of 3 in anhydrous pyridine (0.5 ml) was allowed to react with freshly recrystallized p-bron1ophenylsulfony1 chloride (0.141 g) at room temperature for 1 h. After adding 10 ml water, the solid precipitate was removed by filtration and recrystallized from methanol to yield 0.186 g (76%) of 30, m.p. 101- 102"; [a]DZ2 + 71' (c 1, chloroform); Rr0.35 (10:l benzene-ethyl acetate); r(CDC13) (100 Mc) 2.25 (m, phenyl), 4.28 (d, Jlez = 3.8 Hz, H-1), 5.38 (t, H-2), 5.7-6.5 (m), 7.7 (ni, H-3), 8.65 (two isopropylidene groups).

Anal. Calcd. for C1,Hz5BrO8S: C, 46.25; H, 4.93; Br, 16.20; S, 6.50. Found: C, 46.21: H, 5.14; Br, 16.41:

3-Deo..sy-3-C-"lryclroxyrnetlryl"-1,2-O-isopropylide11e- ~( -~ -~1 /0 f l r0 l l0~e (5)

Selective hydrolysis (I) of the mixture of 3 and 4 (1 .I2 g) using 0.1 N sulfuric acid gave 0.89 g (95 %) of 5, [aIDZ2 + 75" (c 1, chloroforn~); Rf 0.45 (3:l benzene- methanol); r(CDcl3), 4.2 (d, = 3.5 Hz, H-I), 5.22 (t, H-2), 5.8-6.4 (m), 7.8 (m, H-3), 8.55 (d, one iso- propylidene group).

1,5,6-Tri-O-6errzoyl-3-r/eoxy-3-C-"lryclroxy1~~etfryl"-l,2-O- isopropylirlene-a-D-alloJi~ro~rose (6 )

Benzoylation of 0.7 g of 5 in the usual way gave 1.22 g (88%) of 6 which was purified by column chromatog- raphy on silica gel using 10:l benzene-ethyl acetate as developer. Compoi~nd 6 was crystallized from chloroform, m.p. 80-81"; [aID2' + 24" (c 3, chloroforn~); r(CDC13) 2-2.5 (m, phenyl), 4.1 (d, J l , z = 3 . 8 Hz, H-1), 5.15 (t, H-2), 5.2-5.7 (m), 7.8 (ni, H-3), 8.5 (d, isopropylidene group).

Anal. Calcd. for C31H3oO9: C, 68.12; H , 5.53. Found: C, 68.89; H, 5.69.

1,2-Di-O-ace1yl-1,5,6-tri-O-6e~tzoyl-3-deoxy-3-C- "lrydroxymetlry1~'-p(and a-)-D-alloftro~~ose (7)

The benzoate 6 (1.10 g) was acetolyzed for 3 days in the usual way (1, 3) to afford 0.77 g (65%) of 7 as a syrup, [c(]D22 0" (c 2, chloroform); Rf 0.4 (10: 1 benzene- ethyl acetate); r(CDC13) 1.9.2.5 (m, phenyl groups), 3.90 (s, H-1 ; ratio of P:a anonier, about 5:l).

9-(3-Deoxy-3-C-"lrydroxymetlry1~-(and a-)-D- a1loftranosyl)oderritre (10)

A mixture of 0.59 g (0.001 ~nole) of 7, 0.530 g (0.001 mole) of 6-benzamidochloron~ercuripurine (S), 0.3 g of Celite, and 25 n11 of anhydrous xylene was freed of moisture by distilling off the xylene under reduced pressure. To the residue were then added 20 ml of ethylene dichloride and 5 ml of the solvent was distilled off. To the reaction mixture, which was kept under reflux, was then added dropwise a solution of 1,2-dichloroethane (3 ml) and titanium tetrachloride (0.12 ml) and the resulting solution refluxed for 4 h. The cooled reaction mixture was poured with stirring into 25 ml saturated sodii~nl bicarbonate, stirred For a further 0.5 h, filtered, and the Celite cake washed with 3 x 20 ml chloroform. The chloroform extract was washed with 30% aqueous potassium iodide (10 ml) and then water (2 x 20 ml), dried over magnesium sulfate, filtered, and evaporated to dryness. The residue was dissolved in 15 ml methanol, norited, and evaporated to dryness. Extraction of the residue with boiling petroleum ether (30-60") left the solid blocked nucleoside 9 (0.42 g, 56%), Rf 0.3 (1 :2 benzene-ethyl acetate) and r(CDC13), 0.7 (m), 1.4 (m), 2.0 (in), 2.5 (m), 3.9 (s), 5.3 (m), 7.9 (m).

The blocked nucleoside 9 (0.42 g) was allowed to react with 0.1 N methanolic sodium methoxide and the product worked-up as described previously (3) to give after crystallization from 80% aqueous methanol 0.118 g (67%) of the p-D-anomer (lo), n1.p. 23S0, - 12" (c 2, water); h,,,,, (Hz01 261 (E = 12 600); R, (adenine), 0.68 on Whatman No. 1 paper (water as developer); r(Dz0) (60'1, 4.1 (d, Jl*,2r = 3 HZ, H-1'); [@]2,j9 -39Oo, [+Iz5, OC, [+I245 + 145' (C 0.003, water).

Anal. Calcd. for C12H17N505: C , 46.30; H, 5.50; N, 22.50. Found: C, 46.24; H, 5.66; N, 22.70.

The mother liquor from the above recrystallization was evaporated to dryness and the residue then dissolved in 20 ml water. The aqueous solution was twice extracted with 10 n11 portions of ether. The aqueous layer which showed the presence of three fluorescent materials was applied to 10 ml (1 cm diam) of a column of Dowex I x 2 (OH-) resin. Fractionation of the zones was achieved as described previously (3, 8) using water followed by 30% methanol and finally 60% aqueous methanol (each about 100 ml). From the 30% methanol eluant there was obtained an additional amount of 0.023 g of P-D-nucleoside 10. The a-D-anomer Ion, contaminated with a little 0-D-anomer, was obtained from the 60% aqueous methanol eluant. This mixture was separated by preparative paper chromatography using water as developer to afford 0.0124g (4%) of a-D-anonler 10a, having R,, = 0.85; h,,,, (H20) 258 (E = I1 800); [a]D22 = +24' (c 1, water). The 0.r.d. curve of the a-D-anomer showed a positive Cotton effect in the region of 260 mp. An attempt to convert syrupy a-D-anonier 10a into crystalline material led to accidental loss of all material.

Sodi~ttrz Metaperiodate Oxidation and Redtiction of the 8-D-allo-N~tcleoside 10 lo Yield 9-(3-Deoxy-3-C- " l r y r l r . o x y m e t l 1 y l " - ~ - ~ - r i 6 o f u r a r 1 o ~ e (11)

The a-D-nucleoside 10 (0.155 g) was degraded by a previously described procedure (3) to yield on recrystal- lization 0.113 g (81 %) of ribo nucleoside 11, m.p. 213- 214"; [aIDZZ -26" (c 1, water); h,,, (H20) 261 (E =

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ROSENTHAL AND SPRINZL: BRANCHED-CHAIN SUGAR NUCLEOSIDES. IV 4481

13 400); R,,, 0.96; methyl sulfoxide-d6) (100 Mc), 1.66 t.1.c. on silica gel G and each component (0.050 g) was (s, H-2), 1.94 (s, H-8), 2.83 (s, NH2), 4.18 (d, Jl,2 = 2 then deacetylated with methanolic sodium methoxide. Hz, H-1), 4.42 (d), 4.86 (m), 5.52 (m), 6.00 (m), 6.4 (m), Paper chron~atographic examination using ethyl acetate, 7.68 (m, H-3', near methyl sulfoxide peak). pyridine, water 8:2:2 as developer revealed that each

Anal. Calcd. for CllH15N504: C, 46.97; H, 5.36; fraction gave 4 identical spots having RGl 1.1, 1.4, 1.6, N, 24.90. Found: C, 46.94; H, 5.37; N, 24.75. and 2.8. The fastest moving zone was eluted with water

(0.015 g) and had [a],22 + 46" (r 1, water). Rechroma- Direct Conversion of 3 into p-D-0110-Nucleoside 10 tography of this zone after standing for several days

An 0.47 g branched-chain sugar was showed that this component had changed into a mixture subjected to acetolysis in the usual way (3) to yield 0.48 g of compounds which were poorly resolved. Attempts to (67%) of a mixture of at least 3 peracetates. The Rf's of crystallize this compound were unsuccessful. The same the major components of the mixture were 0.62 and 0.55 complicated mixture of compoun~s (by paper chroma- using 1 :1 benzene-ethyl acetate; B ID" 0" (c 2, HCCI,); tography) was obtained when compound 7 was treated T(CDCI~) 3.9 (s), 4.0 (small peak), 4.75 (d, Ji.2 = Hz). with methanolic sodium methoxide. The ratio of these peaks was about 4:1:2. Preparative when c o m p o u n ~ 3 (0.270 g) was hydrolyzed with 1 % t.1.c. of an aliquot of the peracetates gave two com- sulfuric acid (5 ml) at 60" for 1.5 h and the product ponents having different n.m.r.'s (the faster moving worked-up in the usual way, 3 major components having component showed H-1 as a singlet at T 3.90 whereas R~~ of 1.1, 1.4, and 1.86 were obtained. the slower component exhibited the doublet at T 4.75).

An aliq~iot of the mixture of peracetates (0.100 g) was allowed to react with anhydrous hydrogen chloride in Acknowledgments ether (20 ml) at room temperature for I day. After the This work was supported in part by the solvent was removed under reduced pressure 5 ml of National Research Council of Canada and by a anhydrous toluene was added to the residue and the university of ~ ~ i ~ i ~ h columbia ~~~~~~~h G ~ ~ ~ ~ . solvent again removed under vacuum. The resulting glycosyl halide was dissolved in anhydrous xylene and We thank Dr. L. D. for many allowed to react under reflux conditions for 5 h and the discussions of the n.m.r. The authors also thank product worked-up in the usual way (2). Thin-layer the U.S. National Cancer Institute (Grant chromatography of the product (1 :2 benzene-ethyl CA-08382) for carrying out biological tests of acetate) revealed 5 spots. Preparative t.1.c. of the mixture on silica gel G gave 9-(1,2,5,6-tetra-0-acetyl-p-D- the nucleosides. allofuranos~l)-6-benzamido~urine 0.015 g (9%); Rf 0.4. A. RosENTHAL and L. NGUYEN. J. Org. Chem. 34, This nucleoside was recrystallized from methanol, m.p. 1029 (1969). 135-135"; [ a l ~ 2 2 - 18" (c 1, CHCI3); hmax (ethanol) 262 2. A. ROSENTHAL, M. SPRINZL, and H. J. KOCH. Can. mw (E 6400). J. Chem. 47, 3263 (1969).

Anal. Calcd. for C26H2,020N,: N, 12.15. Found: 3. A. ROSENTHAL and M. SPRINZL. Can. J. Chem. N, 12.20. 47, 3941 (1969).

The above blocked nucleoside was allowed to react 4. M. L. WOLFROM, K. MATSUDA, F. KOMITSKY, JR.9 and with sodium methoxide according to the method pre- T. E. WHITELEY. J. Org. Chem. 28, 3551 viously described, h,,. (H20) 261; Rf (adenine) 0.68 zgz.uLsEN and BEHIE 2, (compared directly with authentic 10 on the same sheet 6. H. C. B ~ ~ ~ ~ , K. J, M ~ ~ ~ ~ ~ , L. J. M ~ ~ ~ ~ ~ , J. A. of paper). SNOVER, and G. ZWE~FUL. J. Amer. Chem. Soc. 82,

4233 (1960). Attempts to Prepare Ut~blocked Bratlcl~ecl-cliaitz Srrgars 7. R, J. A ~ ~ ~ ~ ~ ~ , L. D, H ~ ~ ~ , L. H ~ ~ ~ ~ , and K. A. of Cotuporrnd 3 MCLAUCHLAN. J. Chem. Soc. 3699 (1962).

The mixture of peracetates described in the previous 8. A. p. MARTINEZ, W. W. LEE, and L. GOODMAN. section was separated into 2 components by preparative J. Org. Chem. 34, 92 (1969).

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