Synthesis of 4‐Octuloses. Part 6. 4‐Octulose Derivatives, Prepared from L‐Sorbose, as Key Intermediates in the Stereoselective Synthesis of C‐Glycoside and Polyhydroxyindolizidine Analogues.
Reactions of 1 and 12 with p-toluenesulfonyl chloride in pyridine gave the corresponding 1-O-p-toluenesulfonyl derivatives 2 and 13 in yields of 91% and 60%, respectively. Compound 12 was also transformed into 14 by treatment with I2/ Ph3P/imidazole in anhydrous dichloromethane. Treatment of compounds 12 and 13/14 with NaN3 in DMF furnished the respective 1-azido-1-deoxy derivatives 3 and 15, which were then deacetonated to give the free 4-octuloses 4 and 16. These were subsequently hydrogenated in the presence of 10% Pd/C to afford the expected polyhydroxylated branched-chain pyrrolidines 5 and 17. Attempted OH R
4‐Octulose Derivatives, Prepared from L‐Sorbose, as Key Intermediates in the Stereoselective Synthesis of C‐Glycoside and Polyhydroxyindolizidine Analogues
Reactions of 1 and 12 with p-toluenesulfonyl chloride in pyridine gave the corresponding 1-O-p-toluenesulfonyl derivatives 2 and 13 in yields of 91% and 60%, respectively. Compound 12 was also transformed into 14 by treatment with I2/Ph3P/imidazole in anhydrous dichloromethane. Treatment of compounds 12 and 13/14 with NaN3 in DMF furnished the respective 1-azido-1-deoxy derivatives 3 and 15, which were then deacetonated to give the free 4-octuloses 4 and 16. These were subsequently hydrogenated in the presence of 10% Pd/C to afford the expected polyhydroxylated branched-chain pyrrolidines 5 and 17. Attempted OH OMes transformation at C-8 in the N−Cbz-protected pyrrolidines 7 and 19 was unsuccessful and an internal anhydration process took place to yield the corresponding C-glycoside-like furanoses 9 and 20. On the other hand, 23 was transformed into the D-ribo analogue 25 through reduction of the intermediate 4,6-diulose 24. Finally, deprotection of 25 in acid medium to give the free 4-ulose 26, followed by hydrogenation of the latter in the presence of 10% Pd/C in methanol, allowed the preparation of (6S,7S,8S,8aS)-6,7,8-trihydroxy-8a-methoxyindolizidin-3-one (27).
Two new organic reference materials for delta13C and delta15N measurements and a new value for the delta13C of NBS 22 oil.
Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a delta13C value of -26.24 per thousand relative to VPDB and a delta15N value of -4.52 per thousand relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a delta13C value of +37.76 per thousand and a delta15N value of +47.57 per thousand. The delta13C and delta15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (delta13C=+1.95 per thousand ), L-SVEC lithium carbonate (delta13C=-46.48 per thousand ), IAEA-N-1 ammonium sulfate (delta15N=0.43 per thousand ), and USGS32 potassium nitrate (delta15N=180 per thousand ) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of delta13C is better than 0.13 per thousand, and that of delta15N is better than 0.13 per thousand in 100-microg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a delta13C value for NBS 22 oil of -29.91 per thousand, in contrast to the commonly accepted value of -29.78 per thousand for which off-line blank corrections probably have not been quantified satisfactorily.