Stereoselective Synthesis of
C1-C18 Region of Palmerolide A from Tartaric Acid

Kavirayani R. Prasad; Amit B. Pawar

doi:10.1055/s-0029-1219797

LETTER

Stereoselective Synthesis of C1-C18 Region of Palmerolide A from Tartaric Acid

Kavirayani R. Prasad*, Amit B. Pawar
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
Fax: +91(80)23600529; e-Mail: prasad@orgchem.iisc.ernet.in;

Abstract

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Abstract

A stereoselective synthesis of the C1-C18 region of marine natural product palmerolide A from chiral pool tartaric acid is presented. The key synthetic sequence includes the elaboration of a γ-oxo-amide derived from tartaric acid and alkene formation involving Boord type fragmentation.

Key words

Palmerolide A - marine natural product - stereoselective synthesis - tartaric acid

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References

References and Notes

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7

Formation of a minor amount (5%) of diketone resulting from the addition of Grignard reagent to both amide groups was observed

8

Formation of the other diasteromer was not observed within detectable limits by ^¹H NMR

9

All new compounds exhibited satisfactory spectroscopic data. Compound 9: [α]_D -23 (c 0.5, CHCl₃); IR (neat): 3483, 2985, 1718, 1653, 1399 cm^-¹; ^¹H NMR (300 MHz, CDCl₃): δ = 6.89 (dt, J = 15.2, 6.6 Hz, 1 H), 5.78 (dt, J = 15.6, 6.6 Hz, 1 H), 4.12 (q, J = 6.9 Hz, 2 H), 3.90-3.60 (m, 3 H), 3.54 (dd, J = 11.6, 4.6 Hz, 1 H), 2.37-2.28 (br s, 1 H), 2.27-2.12 (m, 2 H), 1.64-1.44 (m, 4 H), 1.35 (s, 3 H), 1.34 (s, 3 H), 1.23 (t, J = 6.9 Hz, 3 H); ^¹³C NMR (100 MHz, CDCl₃): δ = 166.6, 148.4, 121.7, 108.6, 81.3, 76.5, 61.8, 60.1, 32.3, 31.9, 27.3, 26.9, 24.4, 14.2; HRMS: m/z calcd for C₁₄H₂₄O₅Na: 295.1521; found: 295.1519. Compound 11: [α]_D +4.0 (c 1.0, CHCl₃); IR (neat): 3441, 2982, 1721, 1652, 1369 cm^-¹; ^¹H NMR (400 MHz, CDCl₃): δ = 6.95 (dt, J = 15.6, 6.8 Hz, 1 H), 5.95-5.75 (m, 2 H), 5.23 (d, J = 17.2 Hz, 1 H), 5.12 (d, J = 10.4 Hz, 1 H), 4.18 (q, J = 7.1 Hz, 2 H), 4.11 (q, J = 6.0 Hz, 1 H), 2.24 (q, J = 6.0 Hz, 2 H), 1.75-1.62 (br s, 1 H), 1.60-1.43 (m, 4 H), 1.29 (t, J = 7.1 Hz, 3 H); ^¹³C NMR (75 MHz, CDCl₃): δ = 166.7, 148.8, 140.9, 121.6, 114.9, 72.9, 60.2, 36.2, 31.9, 23.7, 14.2; HRMS: m/z calcd for C₁₁H₁₈O₃Na: 221.1154; found: 221.1153. Compound 15: [α]_D +9.4 (c 2.0, CHCl₃); IR (neat): 3079, 2932, 1674, 1382, 1256 cm^-¹; ^¹H NMR (300 MHz, CDCl₃): δ = 5.75 (ddt, J = 16.5, 10.2, 6.3 Hz, 1 H), 5.03-4.83 (m, 2 H), 4.68-4.62 (m, 1 H), 4.54-4.48 (m, 1 H), 3.84-3.70 (m, 1 H), 3.67 (s, 3 H), 3.14 (s, 3 H), 2.24-1.96 (m, 2 H), 1.72-1.55 (m, 1 H), 1.52-1.40 (m, 1 H), 1.38 (s, 3 H), 1.36 (s, 3 H), 0.80 (s, 9 H), 0.01 (s, 6 H); ^¹³C NMR (100 MHz, CDCl₃): δ = 170.4, 138.4, 114.6, 111.0, 80.0, 72.3, 71.5, 61.8, 32.2, 31.9, 29.8, 27.0, 26.2, 25.8, 18.1, -4.5, -4.6; HRMS: m/z calcd for C₁₉H₃₇NO₆SiNa: 410.2339; found: 410.2350. Compound 17: [α]_D -6.0 (c 1.0, CHCl₃); IR (neat): 3469, 2950, 1723, 1657, 1464, 1370 cm^-¹; ^¹H NMR (300 MHz, CDCl₃): δ = 6.86 (dt, J = 15.3, 6.6 Hz, 1 H), 5.73 (d, J = 15.9 Hz, 1 H), 4.08 (q, J = 7.2 Hz, 2 H), 4.00-3.87 (m, 1 H), 3.82-3.53 (m, 4 H), 2.38 (br s, 1 H), 2.37-2.04 (m, 2 H), 1.79-1.62 (m, 1 H), 1.58-1.40 (m, 1 H), 1.30 (s, 3 H), 1.29 (s, 3 H), 1.18 (t, J = 7.2 Hz, 3 H), 0.80 (s, 9 H), 0.10 (s, 6 H); ^¹³C NMR (75 MHz, CDCl₃): δ = 166.5, 148.3, 121.6, 108.8, 79.8, 77.1, 71.4, 62.8, 60.1, 31.1, 28.5, 27.0, 25.8, 18.1, 14.2, -4.2, -4.7; HRMS: m/z calcd for C₂₀H₃₈O₆SiNa: 425.2335; found: 425.2333. Compound 19: [α]_D +15.1 (c 1.8, CHCl₃); IR (neat): 3445, 2925, 2854, 1464, 1256 cm^-¹; ^¹H NMR (300 MHz, CDCl₃): δ = 5.85-5.55 (m, 2 H), 5.32-5.20 (m, 2 H), 4.64 (d, J = 6.6 Hz, 1 H), 4.58 (d, J = 6.6 Hz, 1 H), 4.07 (br d, J = 4.5 Hz, 1 H), 4.02-3.93 (m, 1 H), 3.78-3.63 (m, 1 H), 3.36 (s, 3 H), 2.28-1.92 (m, 2 H), 1.73-1.55 (m, 2 H), 1.53-1.33 (m, 1 H), 0.89 (s, 9 H), 0.08 (s, 3 H), 0.06 (s, 3 H); ^¹³C NMR (75 MHz, CDCl₃): δ = 134.7, 133.1, 129.0, 118.0, 96.6, 79.9, 73.1, 63.8, 55.5, 32.0, 28.2, 25.9, 18.1, -4.2, -4.6; HRMS: m/z calcd for C₁₇H₃₄O₄SiNa: 353.2124; found: 353.2122. Compound 21: [α]_D +21.0 (c 0.8, CHCl₃); IR (neat): 3401, 2953, 1678, 1255, 1036 cm^-¹; ^¹H NMR (400 MHz, CDCl₃): δ = 6.26 (dd, J = 15.0, 10.9 Hz, 1 H), 6.01 (d, J = 10.8 Hz, 1 H), 5.80 (ddd, J = 17.2, 10.5, 6.6 Hz, 1 H), 5.69 (dt, J = 15.0, 6.8 Hz, 1 H), 5.32-5.23 (m, 2 H), 4.68 (d, J = 6.6 Hz, 1 H), 4.60 (d, J = 6.6 Hz, 1 H), 4.05 (br s, 2 H), 4.04-3.96 (m, 1 H), 3.73 (dt, J = 8.2, 4.0 Hz, 1 H), 3.37 (s, 3 H), 2.30-2.06 (m, 2 H), 1.78 (s, 3 H), 1.70-1.62 (m, 1 H), 1.54-1.40 (m, 1 H), 0.9 (s, 9 H), 0.1 (s, 6 H); ^¹³C NMR (100 MHz, CDCl₃): δ = 134.8, 134.7, 134.6, 126.0, 125.2, 118.0, 94.6, 79.8, 73.6, 68.7, 55.5, 32.1, 28.9, 25.9, 18.2, 14.1, -4.2, -4.6; HRMS: m/z calcd for C₂₀H₃₈O₄SiNa: 393.2437; found: 393.2423.