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Synlett 2011(11): 1602-1604  
DOI: 10.1055/s-0030-1260782
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Total Synthesis of Gabosine H

Kavirayani R. Prasad*, S. Mothish Kumar
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
e-Mail: prasad@orgchem.iisc.ernet.in;
Further Information

Publication History

Received 10 February 2011
Publication Date:
10 June 2011 (online)

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Abstract

Stereoselective total synthesis and assignment of the absolute configuration of the keto carba sugar gabosine H is presented. Pivotal reactions in the sequence include desymmetrization of the dimethylamide of tartaric acid and ring-closing metathesis.

Key words

gabosine H - natural products - stereoselective synthesis - ring-closing metathesis

    References and Notes

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5

Formation of minor amounts of 1,4-diketone resulting from the addition of Grignard reagent to both amides is observed.

6

The dr of the product alcohol was estimated to be 9:1 by ¹H NMR.

7

All compounds exhibited satisfactory analytical data.
Compound 5: [α]D -25.5 (c 2.6, CHCl3). IR (neat): 2989, 2938, 1654, 1374, 1157, 1054 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 6.29 (s, 1 H), 6.00 (d, J = 1.0 Hz, 1 H), 5.68 (d, J = 5.8 Hz, 1 H), 4.99 (d, J = 5.8 Hz, 1 H), 3.16 (s, 3 H), 2.98 (s, 3 H), 1.90 (s, 3 H), 1.44 (s, 3 H), 1.43 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 197.4, 168.0, 142.3, 128.8, 112.2, 78.1, 75.1, 37.0, 35.8, 26.3, 26.2, 17.5. HRMS: m/z calcd for C12H19NO4 + Na: 264.1212; found: 264.1205.
Compound 3: mp 74-75 ˚C; [α]D -26.5 (c 1.8, CHCl3). IR (KBr): 3386, 2970, 2984, 2948, 1641, 1057, 1040, 890 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 5.06 (s, 1 H), 4.95 (s, 1 H), 4.82-4.79 (m, 1 H), 4.52 (d, J = 7.0 Hz, 1 H), 4.08 (dd, J = 7.9, 3.0 Hz, 1 H), 3.13 (s, 3 H), 2.96 (s, 3 H), 2.59 (d, J = 8.2 Hz, 1 H), 1.82 (s, 3 H), 1.46 (s, 3 H), 1.38 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 168.7, 144.7, 112.1, 110.6, 78.6, 74.6, 73.7, 37.0, 35.7, 26.8, 26.1, 18.8. HRMS: m/z calcd for C12H21NO4 + Na: 266.1368; found: 266.1357.
Compound 2: [α]D +23.3 (c 1.8, CHCl3). IR (neat): 3459, 2989, 2924, 1699, 1609, 1403, 1374, 1213, 1088, 1061 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 6.82 (ddd, J = 17.4, 10.6, 2.4 Hz, 1 H), 6.45 (ddd, J = 17.4, 2.4, 1.5 Hz, 1 H), 5.86 (ddd, J = 17.4, 2.4, 1.5 Hz, 1 H), 5.04-4.96 (m, 2 H), 4.51-4.49 (m, 1 H), 4.38-4.34 (m, 1 H), 4.13-4.12 (m, 1 H), 2.50-2.48 (br s, 1 H), 1.79 (s, 3 H) 1.49 (s, 3 H) 1.34 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 198.7, 144.1, 131.5, 130.8, 113.0, 111.3, 80.8, 78.7, 74.7, 26.8, 26.0, 18.6. HRMS: m/z calcd for C12H18O4 + Na: 249.1103; found: 249.1101.
Compound 6: mp 122-126 ˚C; [α]D +88.2 (c 1.0, CHCl3). IR (KBr): 3453, 2989, 2929, 2873, 1708, 1378, 1232, 1072, 1059 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 5.86 (s, 1 H), 4.55 (br d, J = 7.4 Hz, 1 H), 4.09 (d, J = 10.7 Hz, 1 H), 3.85 (dd, J = 10.4, 8.4 Hz, 1 H), 3.45-3.25 (br s, 1 H), 2.07 (s, 3 H), 1.46 (s, 6 H). ¹³C NMR (100 MHz, CDCl3): δ = 192.4, 161.3, 125.8, 113.0, 81.4, 79.7, 73.5, 26.8, 26.5, 19.5. HRMS: m/z calcd for C10H14O4 + Na: 221.0790; found: 221.0802.
Gabosine H: mp 118-119 ˚C; [α]D -74.0 (c 0.6, MeOH).
IR (KBr): 3431, 2894, 2876, 1657, 1625 cm-¹. ¹H NMR (400 MHz, CD3OD): δ = 5.92 (s, 1 H), 4.23 (d, J = 8.4 Hz, 1 H), 4.01 (d, J = 10.8 Hz, 1 H), 3.56 (dd, J = 10.8, 2.4 Hz, 1 H), 2.07 (s, 3 H). ¹³C NMR (100 MHz, CD3OD): δ = 199.4, 165.7, 125.0, 79.1, 78.0, 75.1, 20.0. HRMS: m/z calcd for C7H10O4 + Na: 181.0477; found: 181.0477.