3- Hydroxy-4-pentenoate

Another application of this method is the stereoselective addition of (7 )-2-hydroxy-l,2,2-triphenylethyl acetate, via the lithium enolate, to propenal (acrolein) which affords mainly the ester 13 (d.r. 92 8). When the acid, obtained in the subsequent alkaline hydrolysis, is converted into the ammonium salt derived from (.S)-l -phenylethylaminc, and the salt recrystallized once, then the amine liberated (/f)-3-hydroxy-4-pentenoic acid is obtained in 41 % yield [relative to the (/ )-acetate] and >99.8% ee82. 

Polymers containing 3-hydroxy-4-pentenoate, 3HB, and 3HV were synthesized by Rhodospirillum rubrum and a strain of Burkholderia [40,41]. The repeating units found in this PHA included 3HB, 3HV, and 3-hydroxypentenoate (3HP), and the amount of 3HP units was as high as 19%, but no other poly(HASCL)s containing functional group have been reported to date. 

HPE 3-Hydroxy-4-pentenoic acid 3HPV 3-Hydroxyphenylvaleric acid 3HV 3-Hydroxyvaleric acid... 

A. Ethyl 3-hydroxy-4-pentenoate. A dry, 2-L, two-necked, round-bottomed flask, capped with septa and equipped with a thermometer (Note 1), magnetic stirring bar, and an argon inlet is flushed with argon and charged with dry tetrahydrofuran (400 mL, Note 2) and diisopropylamine (30.8 mL, 220 mmol, Note 3). The solution Is cooled to -30°C and butyllithium (BuLi) (93.2 mL, 220 mmol, 2.36 M solution in hexanes, Note 4) is added. The reaction is stirred for 15 min and cooled to -76° to -78°C. Dry ethyl acetate (19.5 mL, 200 mmol, Note 5) is added dropwise so that the Internal reaction temperature remains below -66°C (addition time 10-15 min). When addition of the ethyl acetate is complete, the reaction Is stirred for 50 min at -70° to -78°C. A solutior of freshly distilled acrolein (13.4 mL, 200 mmol, Note 6) and 100 mL of dry... 

Ethyl 3-hydroxy-4-pentenoate 4-Pentenoic acid, 3-hydroxy-, ethyl ester (9) (38996-01-9)... 

The conditions of Jones oxidation are compatible with complex organic compounds containing functional groups such as esters, ketones, amides and alkenes. For example, ethyl 3-hydroxy-4-pentenoate (7.3) on oxidation with Jones reagent gave ethyl 3-oxo-4-pentenoate (Nazarov s reagent) (7.4). 

When 3-hydroxy-Ar,Ar-dimethyl-4-pentenamide32 or its 3-acetoxy derivative are cyclized, the 4,5-cw-isomers in 98% yield and d.r. (cis/trans) 98 2, and 84% yield and d.r. (cisltrans) 86 14, respectively, are obtained. These results are in accordance with the cyclization of 3-hydroxy-4-pentenoic acid performed under kinetic conditions (iodine in diethyl ether/tetrahydrofuran and sodium hydrogen carbonate)32. 

Stereoselective conversion of 2-amino-3-hydroxy-4-pentenoic acid35 into the highly functionalized 2-furanones with the m-(4-hydroxy, 4-haloalkyl) relationship has been obtained through electrophile-promoted cyclization, due to the propensity of the hydroxy group to direct a cis substitution. Thus, treatment of (2.S, 3S)-2-tcrt-butoxycarbonylamino-3-hydroxy-4-pentenoic acid (32) with /V-bromosuccinimide in tetrahydrofuran gives the corresponding (35,4/ ,55 )-bromolactone 33 in 70% yield as the sole product35. 

Under similar cyclization conditions (2S, 3R)-2-/< r/-butoxycarbonylamino-3-hydroxy-4-pentenoic acid (32) gives the corresponding (3S, 4S, 5.R)-bromolactone in low yield. On the contrary, the lactonization performed with mercury(Il) acetate in tetrahydrofuran, followed by treatment with bromine, exclusively produces the (SS S /Q-lactone 33 in 56% yield. The (35,45,5/ )-lactone was converted into (25,3S,4S )-3,4-dihydroxyproline (34), a compound isolated from diatom cell walls. These transformations thus provide an effective method for the synthesis of substituted prolines35. 

Dilactones can be synthesized by a palladium-catalyzed stereospecific intramolecular double cycliza-tion of 3-hydroxy-4-pentenoic acids (Scheme 21). The cis stereochemistry of the reaction is rationalized by assuming that attack of Pd" on the alkene is directed by the allylic OH group, forming the intermediate (12). 

Stereoselective alkoxycarbonylation with lactone formation is achieved in the intramolecular heterocarbonylation of 4-pentene-l,3-diols and 3-hydroxy-4-pentenoic acids57 - 59,97. 

Aminodeoxy sugars are biochemically interesting due to their efficiency as enzyme inhibitors as well as their potential anti-HIV activity. Double deprotonation of 153 and subsequent treatment with acrolein affords 164 as the major diastereomer (92 8). Alkaline hydrolysis of this crude mixture provides (7 )-3-hydroxy-4-pentenoic acid (165) with 83.5% ee. This is easily enhanced by resolution via the (5)-l-phenethylammonium salt, so that 165 can in fact be obtained with 99% ee. lodolactonization of 165 generates the second stereogenic center and provides the furanone skeleton 166, isolated with 97.8% de. Depending on the sequence of transformations chosen, 166 can be converted either to methyl (3i ,47 )-5-amino-2,5-... 

Nakagawa and co-workers performed a synthesis of racemic and both enantiomeric forms of 2-deoxy-eo rliro-pentose from 3-hydroxy-4-pentenoic acid... 

Valentin HE, Berger PA, Gruys KJ, Rodrigues MFD, Steinbuchel A, Tran R, Asrar J (1999) Biosynthesis and characterization of poly(3-hydroxy-4-pentenoic add). Macromolecules 32 7389-7395... 

When the lithium enolate 84 is added to propenal (tvithout transmetala-tion), the diastereomeric esters 87a and 87b are formed in the ratio 92 8. In this reaction the crude mixture 87a/87b tvas hydrolyzed to give the carboxylic acid (R)-88 in 83.5% ee. To obtain the enantiomerically pure 3-hydroxy-4-pentenoic acid, enrichment tvas performed by single recrystallization of the ammonium salt, formed from (S)-l-phenylethylamine. When the amine has been liberated from the salt the carboxylic acid (R)-88 is obtained in >99.8% ee and 41% overall yield (Scheme 1.18) [132]. The (S) enantiomer, but not the ( R) enantiomer, of 3-hydroxy-4-pentenoic acid 88 (both prepared according to this procedure) has been sho vn to be a substrate for the enzyme 3-hydroxybutanoate dehydrogenase - another example of the different biological activity of enantiomeric compounds [133]. 

Procedure (R)-3-Hydroxy-4-pentenoic acid (88) by aldol addition of doubly de-protonated (R)-HYTRA (83) [132]. A 250-mL, tv o-necked, round-bottomed flask is equipped vith a magnetic stirrer, a septum, and a connection to a combined vacuum and nitrogen line. The air in the flask is replaced by nitrogen and dry THF (100 mL) and diisopropylamine (37.7 mL, 0.264 mol)... 

Synthesis of (R)-3-hydroxy-4-pentenoic acid 88 by stereoselective aldol addition of the chiral acetate (R)-83. 

The role, synthesis and depolymerization of PHB in the purple bacterium Rhodospirillum rubrum have been extensively investigated in the past [7, 22, 40]. Now, R. rubrum has recently been used by Ulmer et al. [112] to synthesize unusual polymers containing 3HB, 3HV, and 3-hydroxy-4-pentenoate (3H4PE) repeating units from both 4-pentenoic acid and pentanoic acid. Long growth times and low cell and polymer yields were observed. 

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