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In response to fluctuations in cell-population denseness, many bacteriums regulate a diverse array of physiological activities by a procedure called quorum detection. Quorum feeling bacteriums release autoinducers to modify cistron look that leads to alteration in procedures such as competency, junction, antibiotic production and biofilm formation. In general, Gram-negative bacteriums ( i.e. , Pseudomonas aeruginosa ) use N-acylated homoserine-?-lactones ( 1, PG=acylated concatenation ) as autoinducers [ 1 ] . Cystic Fibrosis ( CF ) is the most common autosomal recessionary upset of Caucasian populations which refers to the characteristic fibrosis and cyst formation within the pancreas. Trouble in external respiration is the most common symptom which consequences from lung infections that are treated with, though non cured by, antibiotics and other medicines. Although, most CF patients survive into maturity through the extended usage of antibiotics, bulk of them succumb to respiratory failure brought on by chronic bacterial infection from Pseudomonas aeruginosa and Burkholderia cepacia. Because of the rise of antibiotic immune strains of bacteria normally found in CF patients, alternate methods are now sought for the intervention of CF and other diseases which needs the usage of antibiotics for the intervention [ 2b ] . One such alternate therapy which uses chemicals that interrupt or destroy quorum detection signals is called signal intervention or quorum extinction. Recent research has shown that bacterium ‘s ability to pass on can be disrupted and thereby disable or decrease the bacterium ‘s ability to go infective [ 2c ] . The organic structure is hence non compromised by cell harm, redness, toxicity or other damaging effects of the bacterium. This gives the organic structure clip to eliminate the bacteriums of course through normal immune system maps [ 2d ] . It seems plausible that such a fresh attack to the intervention of bacterial infections would regards or replaces the usage of antibiotics.

N-Protected homoserine-?-lactones ( 1 ) are besides known for their biological activities against serine proteases every bit good as thiol-containing enzymes [ 3 ] . Further, N-protected homoserine-?-lactones ( 1 ) have been used in legion syntheses of organic natural merchandises and drugs [ 4, 5 ] . They besides serve as a precursor for a figure of synthetically of import compounds such as homoserine derived functions ( 2 ) [ 6 ] , 2-amino-4-halo-butanoic acid derived functions ( 3 ) [ 7 ] and vinyl glycine derived functions ( 4 ) [ 8 ] . ( Scheme 1 )

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Scheme 1 Common organic reactions of N-protected-L-homoserine-?-lactones

Despite their proved value, N-protected homoserine-?-lactones ( 1 ) are really expensive or non even available in their optically pure signifier. For illustration, the cost of N-benzyloxycarbonyl-L-homoserine-?-lactone ( 1b ) is about $ 150/g while the cost of optically impure N-tert-butylcarbonyl-homoserine-?-lactone ( 1a ) is about $ 102/g [ 9 ] . Other N-protected homoserine-?-lactones ( 1 ) are non commercially available from any major chemical provider. Several processs exist for the synthesis of N-protected homoserine-?-lactones ( 1 ) but their commercial scarceness may be due to the deficiency of a common or cheap man-made protocol. N-Protected homoserine-?-lactones ( 1 ) can be obtained from the N-protection of homoserine-?-lactones ( 5 ) under basic conditions [ 10 ] , or from homoserine ( 6 ) via N-protection followed by the cyclization to the lactone [ 11 ] ( Scheme 2 ) . The drawback in these man-made strategies is the high cost of L-homoserine-?-lactone ( 5 ) and L-homoserine [ 9 sigma ] . Alternative methods use relatively inexpensive get downing stuffs such as L-methionine ( 7 ) and L-aspartic acid ( 8 ) { 9 Sigma } . For illustration, N-protected-L-homoserine-?-lactones ( 1 ) can be synthesized by N-protection of L-methionine ( 7 ) followed by refluxing with an alkyl iodide under acidic conditions [ 12a, vitamin D ] or by change overing it to L-homoserine followed by N-protection and cyclization [ 12b ] . While the synthesis from L-methionine can be done in high output and in few stairss, the amino protecting group picks in these methods are non diverse ; for illustration, troubles were observed in the synthesis of N-tert-butoxycarbonyl-L-homoserine-?-lactone [ 14a ] and there are concerns about possible racemization at the reflux temperature [ 14b ] . Alternatively, N-protected-L-homoserine-?-lactones ( 1 ) can besides be synthesized in a multistep process get downing with selective esterification of L-aspartic acid ( 8 ) followed by N-protection, precipitation of the dicyclohexylammonium salts, selective decrease with LiBH4, and cyclization to the corresponding-?-lactones during isolation [ 13 ] . Isolated illustrations of syntheses of N-protected-L-homoserine-?-lactones ( 1 ) from L-aspartic acid based derived functions ( 9-12 ) besides exist in the literature ; nevertheless, these studies did non supply a corporate survey and look to be protecting group specific methods [ method A/B/C- ref15, 16, 17 ] . For illustration, the man-made protocol from 12 to 1 proceeded merely if PG=trifluoroacetyl, otherwise decrease ever led to unsought compound 13 [ 19 ] . Most of these methods besides require extra stairss and usage of unwanted reagents [ method b- ref18 ] ( Scheme 3 ) . For case, man-made protocol from 11 to 1 [ 18 ] , requires the usage of thionyl chloride which is non merely environmentally damaging but besides extremely regulated and non easy available. Besides, usage of metal contact action in this protocol is unwanted in late phases of a drug synthesis [ ref, find which says so ] .

Scheme 2 Comparison of different possible path to synthesise 1. Scheme 3. Man-made paths to 1 from L-aspartic acid based compounds

In visible radiation of the above mentioned troubles, we report an economical and facile manner to synthesise the N-protected-L-homoserine-?-lactones ( 1 ) in a three measure procedure from L-aspartic acid ( 8 ) . Our method involves N-protection of Laˆ?aspartic acid ( 8 ) under basic conditions [ 20 ] , followed by the acid catalyzed condensation with paraformaldehyde to give N-protected-5-oxazolidinone-L-aspartic acid ( 11 ) ( Scheme 4 ) [ 21 ] . While some of the N-protected-5-oxazolidinone-L-aspartic acids ( 11a-b, vitamin D ) could be synthesized in moderate to good outputs by refluxing a mixture of 14, paraformaldehyde and p-toluenesulfonic acid ( p-TsOH ) in methylbenzene or benzine, similar conditions resulted in low output of 11c or did non bring forth expected N-acyl or N-nosyl ( N-2-nitrobenzenesulfonyl ) oxazolidinone compounds ( 11d, degree Fahrenheit ) . Several efforts to obtain 11f by changing equivalents of p-TsOH ( 0.06-1.1 combining weight. ) and paraformaldehyde ( 1-4 combining weight. ) , reaction clip ( 1 hr- overnight ) , dissolvers ( benzine, methylbenzene, THF, DMF, acetic anhydride/acetic acid ) or temperature ( 60-100 & A ; deg ; C or refluxing ) utilizing conventional warming were unsuccessful. The 2-nitrobenzenesulfonyl ( nosyl ) group, introduced by Fukuyama [ 31 ] , is of import because it can be removed under really mild conditions with thiolates. N-Fmoc protection is besides of import from a man-made position whereas N-acyl protected compounds are important for biological surveies as mentioned earlier. Following a lead by Tantry et.al. [ 21g ] where an unmodified domestic microwave was used for the synthesis of related oxazolidinone derived functions, we attempted to utilize a 2.45 GHz CW ( uninterrupted moving ridge ) microwave reactor for the synthesis of the coveted oxazolidinones. Microwave warming ( 300 W, 80-105 & A ; deg ; C, benzine or methylbenzene ) well shortened the reaction clip to 5-15 proceedingss and resulted in systematically good outputs of 11a-f. The best reaction conditions standardized for the synthesis of 11a-f are described in the experimental subdivision. Oxazolidinones 11d and 11f were new compounds while full word picture informations was non reported for 11c and 11e. 1H and 13C NMR informations for 11a besides did non wholly fit with the reported information. A considerable widening was observed for the -CH2COOH protons in the 1H NMR spectra of 11a and 11c, likely due to the presence of rotamers.26a Structures of 11a and 11c were confirmed by roll uping 1H NMR spectra at higher temperatures ( See Supporting Information no ) . N-Acyl-5-oxazolidinone-L-aspartic acid ( 11d ) was obtained as a mixture of two rotamers at room temperature as evidenced by 1H and 13C NMR spectrum which corresponds to two sets of extremums at 295 K. These two set of extremums ( ratio 1/2.5 ) get downing to unify as 1H NMR spectra were collected at higher temperature and eventually, merged wholly when the temperature reached 67 & A ; deg ; C in d5-pyridine ( See Supporting Information no ) . This phenomenon is non surprising, since the presence of rotamers in similar N-acyl-5-oxazolidinone compounds have been reported previously.26b

Scheme 4. Synthesis of N-Protected-5-oxazolidinone-L-aspartic acid ( 11 ) . ( I ) Solvent, base, PG-Cl or PG-anhydride ( two ) Solvent, PTSA, paraformaldehyde. ( a 14a, vitamin D were commercially available )

It is known that the N-protected-Laˆ?aspartic acid derived functions ( 14 ) can be selectively reduced [ 22 ] , hence, it was anticipated that selective decrease of the COOH side concatenation of 11 can be likewise achieved. The N-Cbz-5-oxazolidinone-L-aspartic acid ( 11b ) was chosen for initial experiments due to its higher outputs and stableness. Treatment of 11b with N-methylmorpholine and methyl chloroformate in dry THF at -15 & A ; deg ; C led to the in situ formation of a assorted anhydride ( 15b, PG=Cbz ) and was followed by the add-on of NaBH4 to cut down the side concatenation and organize N-Cbz-5-oxazolidinone-L-homoserine ( 16b, PG=Cbz ) . The reaction was quenched with MeOH and an acid ( dil. HCl or CH3COOH ) to obtain 16b in 61 % output. In an effort to better this output, isobutyl chloroformate was used as an option to methyl chloroformate [ 23 ] , which led to the synthesis of 16b in an improved output of 71 % ( Scheme 5 ) . N-Cbz-5-oxazolidinone-L-homoserine ( 16b ) was further treated with 1.0 M citric acid and was refluxed for 1 hour, which led to the synthesis of 1b in 55 % output ( Scheme 5 ) . The output of 1b was increased to 70 % by subjecting 16b to the following measure without any workup and by increasing the reaction clip to 2-4 h. It was observed that increasing reaction clip ( 20 H ) or utilizing HCl ( 1 M ) alternatively of citric acid ( 1M ) or the usage of LiBH4 alternatively of NaBH4 as the reduction agent, all resulted in lower outputs. N-Tosyl- and N-nosyl-L-homoserine-?-lactone ( 1e, degree Fahrenheit ) were besides obtained in 68 % and 70 % output severally by utilizing a similar protocol. However, this method failed to bring forth any important measures of 1a, c-d, presumptively because of the acerb sensitiveness of the starting substrates ( 11a, c-d ) under refluxing temperatures [ 29 ] .

To find at what stage the job is happening, the reaction of 11c was stopped after decrease measure and 16c was obtained in 82 % output. However, 16c farther decomposes during the cyclization measure under conventional warming conditions. When microwave irradiation ( 300 W, 80 & A ; deg ; C ) was applied to 16c in 1M citric acerb solution, it readily converted to 1c within 10 min. Lactone 1c could be obtained in 80 % output when 16c was subjected to MW conditions without workup or purification at that phase and 1d was likewise obtained in 84 % output utilizing this protocol, while 1b and 1e-f were obtained in moderate outputs.

Scheme 5. Synthesis of N-protected-L-homoserine-?-lactones. ( I ) NMM ( 1.2 eq. ) / IBCF ( 1.2 eq. ) in THF, NaBH4 followed by MeOH ( two ) 1M Citric acid, Method A: refluxing ; Method B: MW, 300 W, 5-15 min. , 80-100 & A ; deg ; C.

The constellation of the stereocenter of 1a-e was assigned to be S by utilizing a assortment of methods. Optical rotary motion values for 1b, 1d and 1e correlated good with literature values [ 24 ] . To corroborate the optical pureness of 1c, racemic 1c was obtained ( Scheme 5 ) . HLPC analysis of racemic 1c on a CHIRACEL-OJ chiral HPLC column revealed two extremums while merely one extremum was observed for 1c, corroborating the optical pureness of 1c.

Scheme 6. Synthesis of racemic N-protected-L-homoserine-?-lactones.

The absolute constellation of antecedently unknown 1f was determined to be S with the aid of individual crystal X-ray analysis ( Figure 1 ) [ 30 ] .

Figure 1. X-ray construction of compound 1f. ( ORTEP diagram with 50 % chance, H atoms have been deleted except at C2 place )

In drumhead, we have developed a new and facile method for the synthesis of N-protected-L-homoserine-?-lactones. This method is an promotion of the old methods and uses inexpensive get downing stuff to bring forth optically pure N-protected-L-homoserine-?-lactones in moderate to high outputs. Use of MW conditions besides provides an advanced synthesis with less reaction clip and less solvent with an oculus on green synthesis.

Experimental: –

N-Protected-L-aspartic acid derived functions ( 14a, vitamin D ) were purchased from Sigma Aldrich. Compounds 14b and 14c were synthesized utilizing reported protocols [ 20 ] . M.P. , IR, 1H NMR, 13C NMR and optical rotary motion for 14b and 14c matched literature studies [ 20 ] .

Synthesis of ( 2S ) -N-Tosylaspartic acid ( 14e ) synthesized following the process from ref [ 20h ] . yield= 92 % , Mp. 112-114 & A ; deg ; C ( illuminated. 114-116 & A ; deg ; C,20h 112-114 & A ; deg ; C20i ) ; : +12.3 & A ; deg ; ( c = 4.0, MeOH ) ( lit. +12.1 & A ; deg ; ( c = 4.0, MeOH ) 20i ) ; 1H NMR ( MeOH-d4 ) ? : 8.13-8.10 ( m, 1H ) , 7.91-7.88 ( m, 1H ) , 7.80-7.77 ( m, 2H ) , 4.42 ( T, J = 5.4 Hz, 1H ) , 2.85 ( m, 2H ) ; 13C NMR ( MeOH-d4 ) ? : ; IR ( neat, ? soap ) : 3500-2500, 3302, 1716, 1595, 1405, 1341, 1305, 1242, 1212, 1186, 1163, 1126, 1089, 1041, 1018, 950, 911 ( cm-1 ) .

Synthesis of ( 2S ) -N-Nosylaspartic acid ( 14f ) To a solution of L-aspartic acid ( 2.0 g, 15.0 mmol ) in aq. NaOH solution ( 16.0 milliliter, 1.20 g, 30.0 mmol ) at 0 & A ; deg ; C was added Ns-Cl ( 3.66 g, 16.5 mmol ) , ( i-Pr ) 2EtN ( 2.87 milliliter, 16.5 mmol ) and propanone ( 16.0 milliliter ) . After stirring for 10 min, the mixture changed from cloudy to unclutter xanthous and was left to stir at RT for 18 hour. The mixture was so diluted with H2O and the aqueous bed was washed with diethyl quintessence ( 3 x 10 milliliter ) . The aqueous bed was so acidified to pH 1 with 1 M HCl and was extracted with EtOAc ( 3 x 10 milliliter ) . The organic beds were so combined, dried over Na2SO4, filtered and concentrated under decreased force per unit area. The Ns protected aspartic acid, 14f, ( 3.18 g, 83 % ) was obtained as xanthous oil after purification by brassy chromatography on silicon oxide gel ( 70 % EtOAc/n-hexane ) . Recrystallization from EtOAc gave 14f as pale xanthous crystals. Mp. 182-184 & A ; deg ; C ; : -92.1 & A ; deg ; ( c = 1, MeOH ) ; 1H NMR ( MeOH-d4 ) ? : 8.13-8.10 ( m, 1H ) , 7.91-7.88 ( m, 1H ) , 7.80-7.77 ( m, 2H ) , 4.42 ( T, J = 5.4 Hz, 1H ) , 2.85 ( m, 2H ) ; 13C NMR ( MeOH-d4 ) ? : 173.8, 173.2, 149.2, 135.4, 135.1, 133.9, 131.7, 126.2, 54.3, 38.5 ; IR ( neat, ? soap ) : 3293, 2990, 2933, 2879, 1706, 1541, 1415, 1404, 1358, 1341, 1298, 1228, 1195, 1160, 1124, 1068, 919 ( cm-1 ) . Elemental

General process for N-Protected-5-oxazolidinone-L-aspartic acid ( 11 )

Method A: – To a solution of 14 ( 1.0 eq. ) in benzine ( 10 mL/mmol for 14a ) or methylbenzene ( 10 mL/mmol for 14b-e ) was added paraformaldehyde ( 2.0 eq. ) and p-TsOH.H2O ( 0.06 eq. ) . The mixture was heated to 60 & A ; deg ; C ( for 14a ) or refluxed ( for 14b-e ) with remotion of H2O utilizing a Dean-Stark trap filled with MgSO4, The reaction was stopped after disappearing of get downing stuff as judged by TLC analysis ( about 1-2 hour, 4hr for 14c ) . The reaction mixture of 14a was cooled to RT and EtOAc was added. The organic bed was washed with aq. K2CO3 ( 0.3 M, 2 milliliter ) and seawater and dried over MgSO4. The solution was filtered and concentrated under decreased force per unit area. Recrystallization from diethyl quintessence provided 11a as a light xanthous solid. For 14b-e, after ingestion of get downing stuff the dissolver was removed under decreased force per unit area and the corresponding oxazolidinones ( 14b-e ) were instantly purified by brassy chromatography on silicon oxide gel utilizing EtOAc/hexanes as the eluant [ 21 ] .

Method B ( Microwave Assisted Method ) : – To a solution of 14 ( 1.0 eq. ) in benzine ( 5 mL/g for 14a-b, d-f ) or methylbenzene ( 5 mL/mmol for 14c ) was added paraformaldehyde ( 7.0 eq. ) and p-TsOH.H2O ( 0.06 eq. ) . The mixture was subjected to micro-cook irradiation ( 300 W ) at 80 & A ; deg ; C ( for 14a-b, d-f ) or 105 & A ; deg ; C ( for 14c ) for 5-15 min. The reaction mixture was concentrated in vacuo and the corresponding oxazolidinones ( 11 ) were instantly purified by brassy chromatography on silicon oxide gel utilizing EtOAc/hexanes as the eluant.

N-Boc-5-oxazolidinone-L-aspartic acid ( 11a ) ( Method A/B )

To a solution of 14a ( 2.00 g for method A or 200 milligram for method B ) in benzene/EtOAc ( 65.0/5.00 milliliter for Method A ) or benzine ( 2 milliliter for method B ) was added paraformaldehyde ( 2.0 eq. , 515 milligram for method A or 7.0 eq. , 231 milligram for method B ) and p-TsOH·H2O ( 0.06 eq. , 89 milligram for method A or 0.06 eq. , 12 milligram for method B ) . The mixture was either refluxed for 2 hour ( method A ) or subjected to micro-cook irradiation ( 300 W ) at 65 & A ; deg ; C for 10 min. 11a was obtained as white solid after workup as reported earlier.21b recrystallization from diethylether. yield= 1.47 g, 70 % ( Method A ) , 130 milligram, 62 % ( Method B ) , Mp. 128-129 & A ; deg ; C ( lit.21b 132-134 & A ; deg ; C ) ; : +151.3 & A ; deg ; ( c = 1, CHCl3 ) ( lit.21b: +153.1 & A ; deg ; ( c = 1, CHCl3 ) ; 1H NMR ( 400 MHz, CDCl3 ) ? : ( at 328 K ) 10.50 ( s, 1 H ) , 5.43 ( vitamin D, J = 2.0 Hz, 1H ) , 5.23 ( vitamin D, J = 3.6 Hz, 1H ) , 4.32 ( s, 1H ) , 3.25-3.15 ( Br, 1H ) , 3.05-3.02 ( two vitamin D, J = 3.0 Hz, 1H ) , 1.49 ( s, 9H ) ; ( at 293 K ) 10.00-8.50 ( Br s, 1 H ) , 5.50-5.42 ( Br, 1H ) , 5.24 ( vitamin D, J = 3.1 Hz, 1H ) , 4.31 ( s, 1H ) , 3.40-3.15 ( Br, 1H ) , 3.09-3.03 ( two vitamin D, J = 2.9 Hz, 1H ) , 1.49 ( s, 9H ) . 13C NMR ( 100 MHz, CDCl3 ) ? : ( at 328 K ) 174.2, 172.0, 152.2, 82.6, 78.8, 78.5,78.2, 51.6, 51.4, 34.5, 28.2, 28.1 ; ( at 293 K ) 175.3, 172.0, 152.2, 82.6, 78.8, 51.7, 34.7, 28.2, IR ( neat, ? soap ) : 3500-2800, 3064, 2980, 2933, 1804, 1712, 1499, 1478, 1398, 1370, 1313, 1290, 1265, 1169, 1141, 1100, 1052, 988, 926, 861, 846, 819, 770, 736, 702, 684 ( cm-1 ) .

N-Cbz-5-oxazolidinone-L-aspartic acid ( 11b ) ( Method A/B )

To a solution of 14b ( 2.00 g for method A or 200 milligram for method B ) in benzine ( 56.0 milliliter or 1 milliliter for method B ) was added paraformaldehyde ( 449 milligram, 2 combining weight. for method A or 157 milligrams, 7 combining weight. for method B ) and p-TsOH·H2O ( 77.0 milligram, 0.06 combining weight. or 8 milligrams, 0.06 combining weight. for method B ) . The mixture was either refluxed for 2 hour ( method A ) or subjected to micro-cook irradiation ( 300 W ) at 80 & A ; deg ; C for 6 min ( method B ) . 11b was obtained as clear oil after purification with brassy chromatography on silicon oxide gel utilizing EtOAc/hexanes ( 3/7 ) as the eluant. Recrystallization from EtOAc/n-hexane gave 11b as a clear crystal. yield= 1.90 g, 91 % ( Method A ) , yield= 182 milligram, 87 % ( Method B ) , Mp. 82-84 & A ; deg ; C ( lit.21e 85-87 & A ; deg ; C ) ; : +124 & A ; deg ; ( c = 3.53, MeOH ) ( lit.21e: +125.7 & A ; deg ; ( c = 3.53, MeOH ) ) ; 1H NMR ( CDCl3 ) ? : 9.78 ( Br s, 1H ) , 7.34 ( s, 5H ) , 5.48 ( Br s, 1H ) , 5.28 ( vitamin D, J = 3.5 Hz, 1H ) , 5.21-5.11 ( m, 2H ) , 4.34 ( s, 1H ) , 3.30-3.02 ( m, 2H ) ; 13C NMR ( CDCl3 ) ? : 175.0, 171.7, 152.9, 135.2, 128.8, 128.4, 78.5, 68.3, 51.4, 34.0 ; IR ( neat, ? soap ) : 3500-2600, 3030, 1802, 1721, 1422, 1360 ( cm-1 ) .

N-Fmoc-5-oxazolidinone-L-aspartic acid ( 11c ) ( Method B )

A mixture of 11c ( 300 milligram ) , paraformaldehyde ( 7.0 eq. , 177 milligram ) and p-TsOH.H2O ( 0.06 eq. , 9 milligram ) in methylbenzene ( 1 milliliter ) was subjected to micro-cook irradiation ( 300 W ) at 105 & A ; deg ; C for 6 min. The reaction mixture was cooled to rt and EtOAc was added. The organic bed was washed with H2O and seawater and dried over MgSO4. The solution was filtered and concentrated under decreased force per unit area. Recrystallization from acetone/CH2Cl2/hexanes ( 2/1/3 ) or EtOAc/n-hexane gave 11c as a white solid. Alternatively, 11c can besides be purified by brassy chromatography on silicon oxide gel utilizing EtOAc/hexanes ( 5/5 ) as the eluant. yield= 263 milligram, 85 % ( Method B ) , Mp. 185-187 & A ; deg ; C ( lit.21g 175-177 & A ; deg ; C ) ; : +103.4 & A ; deg ; ( c = 1, MeOH ) ; 1H NMR ( Acetone-d6, 318 K ) ? : 7.85 ( vitamin D, J = 7.6 Hz, 2H ) , 7.66 ( vitamin D, J = 7.3 Hz, 2H ) , 7.41 ( T, J = 7.4 Hz, 2H ) , 7.33 ( T, J = 7.5 Hz, 2H ) , 5.41 ( vitamin D, J = 3.5 Hz, 1H ) , 5.19 ( s, 1H ) , 4.62-4.53 ( m, 2H ) , 4.33 ( T, J = 5.7 Hz, 1H ) , 4.26 ( m, 1H ) , 2.84 ( Br s, 2H ) ; 13C NMR ( DMSO-d6, 318 K ) ? : 172.1, 171.3, 152.4, 143.6, 140.8, 127.7, 127.2, 127.1, 125.0, 120.1, 77.9, 67.1, 51.4, 46.6, 34.2 ; IR ( neat, ? soap ) : 3300, 3047, 2955, 2923, 1772, 1727, 1692, 1449, 1431, 1411, 1360, 1299, 1260, 1173, 1131, 1053, 1131, 1053, 992 ( cm-1 ) .

N-Acyl-5-oxazolidinone-L-aspartic acid ( 11d ) ( Method B )

A mixture of 14d ( 200 milligram ) , paraformaldehyde ( 7.0 eq. , 231 milligram ) and p-TsOH.H2O ( 0.06 eq. , 12 milligram ) in benzine ( 1 milliliter ) was subjected to micro-cook irradiation ( 300 W ) at 80 & A ; deg ; C for 15 min. The reaction mixture was concentrated in vacuo and 11d was purified by brassy chromatography on silicon oxide gel utilizing EtOAc/hexanes ( 1/1 ) as the eluant. 11d was dissolved in MeOH and added hexanes/diethyl ether. This solution was triturated to obtain white solid after filteration, yield= 160 milligrams, 75 % for two rotamers ( 1/2.5 ) ( Method B ) , Mp. 132-133 & A ; deg ; C ; : +210.2 & A ; deg ; ( c = 1.0, MeOH ) ; 1H NMR ( 300 MHz, 295 K, MeOH-d4 ) ? : 5.68 ( vitamin D, J = 4.6 Hz, 1H* ) , 5.64 ( vitamin D, J = 3.2 Hz, 1H ) , 5.50 ( vitamin D, J = 3.1 Hz, 1H ) , 5.25 ( vitamin D, J = 4.5 Hz, 1H* ) , 4.66 ( vitamin D, J = 3.4 Hz, 1H* ) , 4.50 ( T, J = 3.3 Hz, 1H ) , 3.14 ( ABX, J = 18.2, 4.1, 2.3 Hz, 2H ) , 3.12 ( vitamin D, J = 3.1 Hz, 2H* ) , 2.15 ( s, 3H* ) , 2.07 ( s, 3H ) *Minor rotamer ; 13C NMR ( 100 MHz, MeOH-d4 ) ? : 174.3, 174.0, 173.5, 172.9, 171.7, 170.5, 80.1, 80.1, 53.7, 52.6, 36.6, 34.7, 21.6, 21.3 ; IR ( neat, ?max ) : 3500-2600, 2989, 2955, 2926, 2854, 1791, 1716, 1605, 1462, 1455, 1427, 1413, 1350, 1316, 1288, 1253, 1206, 1184, 1107, 1093, 1058, 1031, 994, 940, 921, 830, 807, 765, 688, 654, 617, 603 ( cm-1 ) . Elemental

N-Tosyl-5-oxazolidinone-L-aspartic acid ( 11e ) ( Method A/B )

A mixture of 14e ( 200 milligram ) , paraformaldehyde ( 2.0 eq. , 42 milligram for Method A ; 7.0 eq. , 146 milligram for Method B ) and p-TsOH.H2O ( 0.06 eq. , 7 milligram ) in methylbenzene ( 6 milliliter for method A and 1 milliliter for method B ) was refluxed for 3 hour or subjected to micro-cook irradiation ( 300 W ) at 100 & A ; deg ; C for 5 min. The reaction mixture was concentrated invacuo and 11e was purified by brassy chromatography on silicon oxide gel utilizing EtOAc/hexanes ( 7/3 to 3/7 ) as the eluant. gluey solid, yield= 137 milligram, 66 % ( Method A ) , 150 milligram, 72 % ( Method B ) , Mp. 117-118 & A ; deg ; C ( lit.21i 130-131 & A ; deg ; C ) ; : +252 & A ; deg ; ( c = 1.0, Acetone ) ; 21i 1H NMR ( 300 MHz, CDCl3 ) ? : 8.41 ( Br s, 1H ) , 7.93 ( m, J = 8.2 Hz, 2H ) , 7.40 ( m, J = 8.0 Hz, 2H ) , 5.38 ( Doctor of Divinity, J = 5.1 Hz, 2H ) , 4.06 ( T, J = 3.6 Hz, 1H ) , 3.16 ( vitamin D, J = 3.7 Hz, 2H ) , 2.46 ( s, 3H ) ; 13C NMR ( 100 MHz, CDCl3 ) ? : 175.0, 170.9, 145.8, 132.0, 130.58, 127.7, 79.6, 52.9, 36.2, 21.6 ; IR ( neat, ?max ) : 3500-2500, 3241, 3092, 3062, 2986, 2930, 1803, 1718, 1597, 1493, 1401, 1357, 1307, 1293, 1268, 1215, 1165, 1105, 1045, 966, 922, 817, 761 ( cm-1 ) .

N-Nosyl-5-oxazolidinone-L-aspartic acid ( 11f ) ( Method B )

A mixture of 14f ( 200 milligram ) , paraformaldehyde ( 7.0 eq. , 132 milligram ) and p-TsOH.H2O ( 0.06 eq. , 3.2 milligram ) in benzine ( 1 milliliter ) was subjected to micro-cook irradiation ( 300 W ) at 80 & A ; deg ; C for 10 min. The reaction mixture was concentrated in vacuo and 11f was purified by brassy chromatography on silicon oxide gel utilizing EtOAc/hexanes ( 1/1 ) and EtOAc as the eluant. The solid was recrystallised with ethyl ethanoate /diethyl quintessence to give awhite solid, yield= 178 milligram, 86 % ( Method B ) , Mp. 180-181 & A ; deg ; C ; : +232.4 & A ; deg ; ( c = 1.0, MeOH ) ; 1H NMR ( 400 MHz, MeOH-d4 ) ? : 8.21-8.19 ( m, 1H ) , 7.93-7.86 ( m, 3H ) , 5.73 ( vitamin D, J = 4.5 Hz, 1H ) , 5.43 ( Doctor of Divinity, J = 4.5 Hz, J = 0.7 Hz, 1H ) , 4.61 ( T, J = 3.5 Hz, 1H ) , 3.04 ( ABX, J = 18.1 Hz, J = 4.2 Hz, J = 3.4 Hz, 2H ) ; 13C NMR ( 400 MHz, MeOH-d4 ) ? : 173.0, 149.8, 136.7, 133.8, 132.2, 131.4, 126.0, 80.7, 54.6, 36.6 ; IR ( neat, ?max ) : 3500-2500, 3101, 3024, 2955, 2930, 2854, 1793, 1763, 1726, 1540, 1406, 1372, 1330, 1301, 1223, 1201, 1170, 1127, 1101, 1050, 1041, 971, 852, ( cm-1 ) .

Synthesis of N-Cbz-5-oxazolidinone-L-homoserine ( 16b ) 28

This protocol was adapted from a old method.27 To a solution incorporating 11b ( 500 mg 1.78 mmol, 1.0 combining weight. ) and distilled THF ( 20 milliliter ) at -15 & A ; deg ; C was added NMM ( 235 µL, 2.14 mmol, 1.2 combining weight. ) and IBCF ( 282 µL, 2.14 mmol, 1.2 eq. ) . The mixture was left to stir under Ar for 30 min at -15 & A ; deg ; C. NaBH4 ( 0.203 g, 5.35 mmol, 3.0 combining weight. ) was so added in one part followed by MeOH ( 20.0 milliliter ) , which was added dropwise to the mixture over a period of 10 min at 0 & A ; deg ; C. The solution was stirred for extra 10 min, and so neutralized with 1 M HCl ( 1 milliliter ) . The organic dissolvers were evaporated under decreased force per unit area while doing certain the H2O bath did non transcend 35-40 & A ; deg ; C. EtOAc ( 25 milliliter ) was added to the mixture and the organic bed was washed consecutively with 0.1 M HCl ( 2 milliliter ) , H2O ( 5 milliliter ) , 5 % aq NaHCO3 ( 5 milliliter ) , H2O ( 2 x 5 milliliter ) , dried over MgSO4 and concentrated under decreased force per unit area. The merchandise was farther purified straight by flash chromatography on silicon oxide gel ( 50 % EtOAc/hexane ) go forthing the merchandise as a clear oil ( 335 milligram, 72 % output ) . 1H NMR ( CDCl3 ) ? : 7.32 ( s, 5H ) , 5.15 ( s, 2H ) , 4.88 ( Br s, 1H ) , 4.80 ( vitamin D, J = 11.2 Hz, 1H ) , 4.57-4.47 ( m, 3H ) 4.24-4.21 ( m, 2H ) , 3.61 ( Br s, 1H ) , 2.49 ( Br s, 2H ) ; 13C NMR ( CDCl3 ) ? : 175.17, 174.71, 154.80, 135.55, 135.18, 128.41, 128.17, 128.06, 127.85, 72.29, 71.78, 68.07, 67.81, 65.88, 65.41, 56.04, 55.33, 27.43, 26.85 ; IR ( neat, ? soap ) : 3446 ( Br ) , 2956, 1779, 1705, 1482, 1436, 1355, 1258, 1184, 1024, 737, 700 ( cm-1 ) MS, ESI, m/z ( % ) : 288 ( [ M+Na ] + , 100 ) ; HRMS, CI ( +ve ) , m/z: calcd for C12H13NO4 [ M-H2CO ] + : 235.0845 ; found: 235.0836.

Synthesis of N-Fmoc-5-oxazolidinone-L-homoserine ( 16c )

This protocol was adapted from the old method.27 To a solution incorporating 11c ( 380 milligram, 1.03 mmol, 1.0 combining weight. ) and distilled THF ( 10 milliliter ) at -15 & A ; deg ; C was added NMM ( 125 µL, 1.14 mmol, 1.1 combining weight. ) and IBCF ( 150 µL, 1.14 mmol, 1.1 eq. ) . The mixture was left to stir under Ar for 30 min at -15 & A ; deg ; C. Afterwards, the mixture was so cooled to -78 & A ; deg ; C where upon NaBH4 ( 117 milligram, 3.10 mmol, 3.0 combining weight. ) was added in one part, followed by the dropwise add-on of MeOH ( 10.0 milliliter ) . The mixture was left to stir at -78 & A ; deg ; C for 1.5 hour and so quenched with the add-on of 1-2 milliliter of AcOH. The mixture was so stirred for an extra 30 min at -78 & A ; deg ; C before warming to RT. The organic dissolvers were evaporated under decreased force per unit area while doing certain the H2O bath did non transcend 35-40 & A ; deg ; C. To the mixture was added EtOAc ( 25 milliliter ) and the organic bed was washed 0.1 M HCl ( 2 milliliter ) , H2O ( 5 milliliter ) , 5 % aq NaHCO3 ( 5 milliliter ) , H2O ( 2 x 5 milliliter ) , dried over Na2SO4 and concentrated under decreased force per unit area. The merchandise was farther purified straight by flash chromatography on silicon oxide gel ( 50 % EtOAc/hexane ) go forthing the merchandise as a clear oil ( 230 milligram, 63 % output ) . 1H NMR ( 400 MHz, CDCl3 ) 13C NMR ( CDCl3, 313K ) ? : 174.81, 154.85, 143.5, 143.3, 141.2, 127.8, 127.7, 127.1, 124.8, 124.5, 119.9, 119.8, 71.9, 67.7, 65.8, 56.2, 47.1, 27.1 ; IR ( neat, ? soap ) : 3445, 3065, 2962, 2917, 1780, 1704, 1479, 1451, 1391, 1370, 1354, 1254, 1180, 1102, 1023, 952, 810, 761, 740 ( cm-1 ) ; MS, ESI, m/z ( % ) : 376 ( [ M+Na ] + , 100 ) ; HRMS, ESI ( +ve ) , m/z calcd for C20H19NO5Na [ M+Na ] + : 376.1161 ; found: 376.1148.

General process for the readying of N-protected-L-homoserine-?-lactones ( 1 )

Method A: To a dry THF ( 40.0 mL/g ) solution of 11 ( 1.0 eq. ) at -10 to -15 & A ; deg ; C was added Naˆ?methylmorpholine ( 1.2 eq. ) and isobutyl chloroformate ( 1.2 eq. ) . The mixture was left to stir under N for 30 min at -15 & A ; deg ; C. NaBH4 ( 3.0 eq. ) was so added in one part and the reaction was stirred for 15-20 min followed by the dropwise add-on of methyl alcohol ( 40.0 mL/g ) , and the stirred for extra 10 min at 0 & A ; deg ; C, and so neutralized with 1 M acetic acid or citric acid until solution becomes clear ( pH=5-7 ) . The organic dissolvers were evaporated under decreased force per unit area while doing certain the H2O bath did non transcend 35-40 & A ; deg ; C. To the dressed ore was added 1.0 M citric acid ( ~10 mL/g ) and the mixture was refluxed for 2-4 hour and so cooled to rt. It was rapidly extracted with ethyl ethanoate ( 4 ten ) . The organic beds were combined and washed with H2O, seawater, dried over MgSO4, filtered and concentrated under decreased force per unit area. The corresponding lactones, 1 were obtained after purification by brassy chromatography on silicon oxide gel ( hexanes/ethyl ethanoate ) .

Method B ( Microwave Assisted Method ) : – To a dry THF ( 40.0 mL/g ) solution of 11 ( 1.0 eq. ) at -10 to -15 & A ; deg ; C was added Naˆ?methylmorpholine ( 1.2 eq. ) and isobutyl chloroformate ( 1.2 eq. ) . The mixture was left to stir under N for 30-45 min at -10 & A ; deg ; C. NaBH4 ( 3.0 eq. ) was added in one part and the reaction was allowed to slowly warm while it stirred for 15-20 min followed by the dropwise add-on of methyl alcohol ( 50.0 mL/g ) , and the stirred for extra 10 min at 0 & A ; deg ; C, and so neutralized with 1 M acetic acid ( ~ 8 mL/g ) until solution becomes clear ( pH ~ 7 ) . The reaction mixture was so concentrated in vacuo, transferred to a microwave phial with the aid of extra methyl alcohol and the solvent rapidly evaporated in vacuo without exposing it to the heat ( & A ; lt ; 40 & A ; deg ; C ) . The reaction mixture was so added 0.5-1M citric acid ( ~ 4-6 mL/g ) solution and the mixture was exposed to the microwave irradiation ( 300W ) for 5-10 min at 80 & A ; deg ; C. The mixture was extracted with ethyl ethanoate ( 4 ten ) . The organic beds were combined and washed with H2O, seawater, dried over MgSO4, filtered and concentrated under decreased force per unit area. The corresponding lactones, 1 were obtained after purification by brassy chromatography on silicon oxide gel ( hexanes/ethyl ethanoate ) .

N-Cbz-L-homoserine-?-lactone ( 1b ) A solution of 11b ( 200 milligram ) in dry THF ( 8.0 milliliter ) was treated with NMM ( 1.2 eq. , 94 µL ) and IBCF ( 1.2 eq. , 113 µL ) , followed by the add-on of NaBH4 ( 3.0 eq. , 80 milligram ) and so, quenched with MeOH ( 10.0 milliliter ) and 1 M acetic acid ( 1.5 milliliter ) . The dissolver was evaporated in vacuo and added 1M citric acid ( 4 milliliter for Method A or 1 milliliter for Method B ) . The reaction mixture was either refluxed for 2 hour ( Method A ) or exposed to the microwave irradiation ( 300W ) for 15 min at 80 & A ; deg ; C. After the general workup process, 1b was purified by brassy chromatography on silicon oxide gel utilizing hexanes/ethyl ethanoate ( 7/3 to 1/1 ) as eluent. Recrystallization from EtOAc/n-hexane gave 11b as white acerate leafs. yield= 118 milligram, 70 % ( Method A ) , 109 milligram, 65 % ( Method B ) , , Mp. 122-124 & A ; deg ; C ( lit.16 126-127 & A ; deg ; C ) ; : -32.1 & A ; deg ; ( c = 1.0, MeOH ) ( lit.16: -30.5 & A ; deg ; ( c = 1.0, MeOH ) ) ; 1H NMR ( 400 MHz, CDCl3 ) ? : 7.33 ( s, 5H ) , 5.39 ( Br s, 1H ) , 5.11 ( s, 2H ) , 4.44-4.35 ( m, 2H ) , 4.24-4.17 ( m, 1H ) , 2.78-2.70 ( m, 1H ) , 2.26-2.11 ( m, 1H ) ; 13C NMR ( 100 MHz, CDCl3 ) ? : 175.1, 156.0, 135.8, 128.4, 128.1, 128.0, 67.1, 65.6, 50.2, 29.6 ; IR ( neat, ?max ) : 3328, 3058, 3029, 2944, 1778, 1695, 1542, 1385, 1298, 1265, 1225, 1180, 1073, 1013, 1007, 946 ( cm-1 ) .

N-Fmoc-L-homoserine-?-lactone ( 1c ) A solution of 11f ( 200 milligram ) in dry THF ( 8.0 milliliter ) was treated with NMM ( 1.2 eq. , 73 µL ) and IBCF ( 1.2 eq. , 105 µL ) , followed by the add-on of NaBH4 ( 3.0 eq. , 62 milligram ) and so, quenched with MeOH ( 10.0 milliliter ) . The dissolver was rapidly evaporated in vacuo and added 0.5 M citric acid ( 2 milliliter ) . The reaction mixture was exposed to the microwave irradiation ( 300W ) for 10 min at 80 & A ; deg ; C. After the general workup process, 1f was purified by brassy chromatography on silicon oxide gel utilizing hexanes/ethyl ethanoate ( 1/1 ) as eluent followed by recrystallization from 95 % EtOH, white solid, yield= 141 milligram, 80 % ( Method A ) , Mp. 208-209 & A ; deg ; C ( Lit.7b 208-209 & A ; deg ; C ) ; : +12.0 & A ; deg ; ( c = 0.25, CHCl3 ) ; 1H NMR ( 400 MHz, CDCl3 ) ? : 7.76 ( vitamin D, J = 7.5 Hz, 2H ) , 7.58 ( vitamin D, J = 7.4 Hz, 2H ) , 7.40 ( T, J = 7.4 Hz, 2H ) , 7.31 ( T, J = 7.4 Hz, 2H ) , 5.39 ( Br s, 1H ) , 4.47-4.41 ( m, 4H ) , 4.26-4.20 ( m, 3H ) , 2.78 ( m, 1H ) , 2.20 ( m, 1H ) ; 13C NMR ( 100 MHz, CDCl3 ) ? : 174.9, 156.1, 143.7, 143.6, 141.3, 127.8, 127.1, 125.0, 120.0, 67.3, 65.8, 50.5, 47.1, 30.5 ; IR ( neat, ?max ) : 3328, 3061, 3017, 2948, 2918, 2851, 1789, 1686, 1534, 1461, 1384, 1243, 1285, 1263, 1222, 1187, 1161, 1103, 1081, 1017, 995, 971, 947, 909, 756, 738, 692, 644, 621 ( cm-1 ) . Elemental

N-Acyl-L-homoserine-?-lactone ( 1d ) 32 A solution of 11d ( 200 milligram ) in dry THF ( 8.0 milliliter ) was treated with NMM ( 1.2 eq. , 142 µL ) and IBCF ( 1.2 eq. , 121 µL ) , followed by the add-on of NaBH4 ( 3.0 eq. , 121 milligram ) and so, quenched with MeOH ( 10.0 milliliter ) and 1 M acetic acid ( 1.5 milliliter ) . The dissolver was evaporated in vacuo and added 1M citric acid ( 1 milliliter ) . The reaction mixture was exposed to the microwave irradiation ( 300W ) for 15 min at 80 & A ; deg ; C. The reaction mixture was cooled to RT and aq. NaHCO3 was added to make the pH~7. It was extracted with ethyl ethanoate ( 4 ten ) . The organic beds were combined and washed with H2O, seawater, dried over MgSO4, filtered and concentrated under decreased force per unit area. 1d was purified by brassy chromatography on silicon oxide gel utilizing EtOAc and EtOAc/MeOH ( 95/5 ) as eluent followed by repeated recrystallization from CH2Cl2/hexanes, topographic point sensing in I2-Chamber, white solid, yield= 137 milligram, 84 % ( Method B ) , Mp. 82-84 & A ; deg ; C ( Lit.32b 82-84 & A ; deg ; C ) ; : -69 & A ; deg ; ( c = 1.6, DMF ) ( Lit. -69.0 & A ; deg ; , c = 1.6, DMF 32c ; -54.7 & A ; deg ; , DMF32d ) ; 1H NMR ( 400 MHz, CDCl3 ) 32e ? : 6.13 ( s, 1H ) , 4.61-4.54 ( m, 1H ) , 4.48 ( m, 1H ) , 4.32-4.25 ( m, 1H ) , 2.89-2.82 ( m, 1H ) , 2.28-2.11 ( m, 1H ) , 2.08 ( s, 3H ) ; 13C NMR ( 100 MHz, CDCl3 ) ? : 175.8, 170.9, 170.8, 66.0, 48.8, 48.7, 29.4, 22.6, 22.5 ; IR ( neat, ?max ) : 3305, 3072, 2991, 2920, 1777, 1656, 1542, 1450, 1431, 1379, 1300, 1221, 1180, 1154, 1020, 951, 816, 791, 749, 708, 669, 651, 597 ( cm-1 ) .

N-Tosyl-L-homoserine-?-lactone ( 1e ) A solution of 11f ( 250 milligram ) in dry THF ( 10.0 milliliter ) was treated with NMM ( 1.2 eq. , 111 µL ) and IBCF ( 1.2 eq. , 134 µL ) , followed by the add-on of NaBH4 ( 3.0 eq. , 95 milligram ) and so, quenched with MeOH ( 12.5 milliliter ) and 1 M acetic acid ( 2 milliliter ) . The dissolver was evaporated in vacuo and added 1M citric acid ( 5 milliliter for Method A or 1.5 milliliter for Method B ) . The reaction mixture was either refluxed for 2 hour ( Method A ) or exposed to the microwave irradiation ( 300W ) for 10 min at 65 & A ; deg ; C. After the general workup process, 1f was purified by brassy chromatography on silicon oxide gel utilizing hexanes/ethyl ethanoate ( 7/3 to 1/1 ) as eluent followed by recrystallization from CH2Cl2/hexanes, white crystals, yield= 145 milligrams, 68 % ( Method A ) , 100 milligram, 46 % ( Method B ) , Mp. 129-130 & A ; deg ; C ( Lit.12a 130-133 & A ; deg ; C ) ; : +8.5 & A ; deg ; ( c = 1.0, MeOH ) ; 12a 1H NMR, 13C NMR and IR matched with the literature.25a

N-Nosyl-L-homoserine-?-lactone ( 1f ) A solution of 11f ( 200 milligram ) in dry THF ( 8.0 milliliter ) was treated with NMM ( 1.2 eq. , 81 µL ) and IBCF ( 1.2 eq. , 97 µL ) , followed by the add-on of NaBH4 ( 3.0 eq. , 69 milligram ) and so, quenched with MeOH ( 10.0 milliliter ) and 1 M acetic acid ( 1.5 milliliter ) . The dissolver was evaporated in vacuo and added 1M citric acid ( 4 milliliter for Method A or 1 milliliter for Method B ) . The reaction mixture was either refluxed for 2 hour ( Method A ) or exposed to the microwave irradiation ( 300W ) for 5-10 min at 80 & A ; deg ; C. After the general workup process, 1f was purified by brassy chromatography on silicon oxide gel utilizing hexanes/ethyl ethanoate ( 1/1 ) as eluent followed by recrystallization from CHCl3, transparent crystals, yield= 121 milligrams, 70 % ( Method A ) , 73 milligram, 42 % ( Method B ) , Mp. 131-132 & A ; deg ; C ; : -350 & A ; deg ; ( c = 0.1, CHCl3 ) ; 1H NMR ( 400 MHz, CDCl3 ) ? : 8.16 ( m, 1H ) , 7.97 ( m, 1H ) , 7.80-7.75 ( m, 2H ) , 6.16 ( vitamin D, J = 5.7 Hz, 1H ) , 4.47 ( vitamin D, J = 9.0 Hz, 1H ) , 4.30-4.23 ( m, 2H ) , 2.77-2.83 ( m, 1H ) , 2.34-2.45 ( m, 1H ) ; 13C NMR ( 100 MHz, CDCl3 ) ? : 173.8, 147.8, 134.1, 133.8, 133.2, 130.8, 125.9, 66.0, 52.7, 31.0 ; IR ( neat, ?max ) : 3345, 3089, 2998, 2960, 2924, 2883,1782, 1593, 1539, 1442, 1376, 1355, 1221, 1167, 1124, 1058, 1021, 999, 953, 912, 854, 798 ( cm-1 ) . Elemental

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