Micellar diastereoselectivity - tripeptide substrates

Kinetic stereoselectivities are reported for the micelle-catalyzed basic esterolyses of the four diastereomeric ,$\text{Z}$-($\text{D}$ or $\text{L}$)-Phe-($\text{D}$ or $\text{L}$)-Phe-($\text{L}$)-Pro $\text{p}$-nitrophenyl esters.     

Synthesis of the n-benzoyl derivatives of L-arabino,L-xylo and L-lyxo (L-vancosamine) isomers of 2,3,6-trideoxy-3-C-methyl-3-aminohexose from a non-carbohydrate precursor

The synthesis of the N-benzoyl derivatives of $\text{L}$-$\text{arabino}$ (10),$\text{L}$-$\text{xylo}$ (13) and $\text{L}$-$\text{lyxo}$ ($\text{L}$-vancosamine) (12) 2,3,6-trideoxy-3-$\text{C}$-methyl-3-aminohexose from the (2$\text{S}$,3$\text{R}$) diol (1) prepared in fermenting bakers' yeast from α-methylcinnamaldehyde and acetaldehyde is reported     

Anionic tricarbonyl derivatives of molybdenum and tungsten and their reactions with allyl halides

A series of carbonylmetallate anions $\text{fac}$-[MX(CO)₃L₂]^?, where M = Mo or W, X = Cl, Br or I and L₂ = 1,10-phenanthroline(phen) or 2,2′-bipyridine(bipy) have been prepared from the corresponding $\text{cis}$-M(CO)₄L₂ complexes. No evidence of $\text{fac}$-to $\text{mer}$-isomerisation was evident on dissolution, although in MeCN solvolysis occurred with the formation of $\text{fac}$-M(CO)₃L₂(MeCN). Reaction of the anions with various allyl halides resulted in high yields of η³-allyl complexes [MX(CO)₂(η³-RC₃H₄)L₂]. The significance of these observations for the mechanism of the allyl oxidative-addition reaction are discussed.     

Models that demonstrate peptide bond formation by prior thiol capture I. Capture by disulfide formation

Unsymmetrical disulfides formed from $\text{L}$-cysteine esters and $\text{o}$-Cbz-$\text{L}$-alaninyloxy-benzenethiol $\text{9}$, 2-Cbz-$\text{L}$-alaninyloxy-5-chlorophenylmethylenethiol $\text{8}$,4-acetoxyxanthenylmethylene thiol $\text{10}$, and 1,5-diacetoxy-2-methyl-3-methoxy-4-thioxanthone $\text{11}$ are observed to undergo intramolecular O,N-acyl transfer in yields up to 60%, with accompanying disulfide interchange. The significance of these results for a general amide forming strategy of prior cysteine capture are discussed.     

Amino acid derivatives that stabilize secondary structures of polypeptides : II. The most stable conformation of peptides containing 3-amino-2-piperidone-6-carboxylic acid (Acp)

From ¹H NMR evidence, the conformation of the piperidone ring of 3-amino-6-carboxyl-2-piperidone (ACP) in the derivatives Ac-Acp-NHET. Cbz-Gly-Acp-OEt, Cbz-Gly-Acp-Gly-OEt, Boc-$\text{L}$-Phe-$\text{LL}$-Acp-$\text{L}$-Ala-OCH₃, and Boc-$\text{L}$-Phe-$\text{DD}$-Acp-$\text{L}$-Ala-OCH₃ is shown to be a chair with the RCONH function equatorially and the CONHR′ function axially disposed. An internal hydrogen bond of the β-turn type is proposed for these amide derivatives.     

Diastereoselective synthesis of N-acetyl-D,L-acosamine and N-benzoyl-D,L-ristosamine

N-Acyl derivatives of $\text{D}$,$\text{L}$-acosamine and $\text{D}$,$\text{L}$-ristosamine were synthesized with high stereo selectivity utilizing intramolecular Michael addition of γ- and δ-carbomoyloxy-α,β-unsaturated esters.     

On the steric course of the addition of diallylzinc onto α,β-dialkoxy chiral carbonyl compounds: stereospecific synthesis of 2,6-dideoxysugars of the L-series

The synthesis of the 2,6-dideoxy sugars $\text{L}$-digitoxose (14), 2-deoxy-$\text{L}$-fucose (15) and $\text{L}$-mycarose (16) from the C₄ and C₅ chiral synthons (1), (2) and (3), through the intermediacy of the C₇ adducts (4), (8) and (12), obtained by $\text{erythro}$ addition of diallylzinc onto (1), (2) and (3), is reported.     

Synthesis of the serine equivalent, (2R) and (2S)-amino-3-butenol derivatives. Synthetic approaches to the metal chelating poly-amino acid, “aspergillomarasmine A”

Chiral synthons, equivalent to the C₃ amino acid serine, were synthesized in both (2$\text{R}$) and (2$\text{S}$) form from $\text{D}$ or $\text{L}$-methionine respectively; Utilization of this synthon in the construction of metal chelating poly-amino acid aspergillomarasminea A skeleton is presented.     

Reversal of diastereofacial selectivity in the intramolecular michael addition of -α-carbamoyloxy-α,β-unsaturated esters. Synthesis of N-benzoyl-D,L-daunosamine

Contrary to the precedents, 1,3-anti stereoselection was found in the intramolecular Michael addition of ethyl $\text{threo}$,5-carbamoyloxy-4-trialkylsilyloxy-2-hexenoate to culminate in a synthesis of N-benzoyl-$\text{D}$,$\text{L}$-daunosomine. The antiperiplanar effect due to the group at 4-position was revealed to play a major role in the stereoselection in this type of reactions. N-benzoyl-$\text{D}$,$\text{L}$-3-epidaunosamine was also synthesized by 1,2-syn asymmetric induction.     

A facile three-step synthesis of a racemic 4,5-diamino-dideoxy-α-D, β-L-lyxopyranose.

Diels-Alder cycloaddition of nitrosobenzene to 1-methoxycarbonyl-1,2-dihydropyridine led in high yield to the endocyclic hydroxylamine adduct $\text{5}$, which was successively oxydized with potassium permanganate and hydrogenolyzed to give the new aminosugar 4,5-dideoxy-5-methoxycarbonylamino-4-phenylamino-α-$\text{D}$, β-$\text{L}$ lyxopyranose $\text{7}$.     

Synthesis of homoleptic tris(organo-chelate)iridium(III) complexes by spontaneous ortho-metallation of electronrich olefin-derived N,N′-diarylcarbene ligands and the X-ray structures of fac-[Ir{CN(C6H4Me-p) (CH2)2NC6H3Me-p}3] and mer-Ir{CN(C6H4Me-p)(CH2)2NC6H3Me-p}2 {CN(C6H4Me-p)(CH2)2NC6H4Me-p}Cl (a product of HCl cleavage)

Treatment of [{Ir(COD)(μ-Cl)}₂] with excess of the electron-rich olefin [$\text{CN(Ar)(CH}{}_2\text{)}{}_2\text{N}$Ar]₂ (abbreviated as (L^Ar)₂, Ar = C₆H₄Me-p or C₆H₄OMe-p) affords the ortho-metallated tricycle [$\text{Ir(L}{}^{\mathrm{A}}\text{r}$)₃], which for Ar = C₆H₄Me-p (Ia) with HCL yields [$\text{Ir(L}{}^{\mathrm{A}}\text{r}$)₂(L^Ar)]Cl (IV); X-ray data show that in IV there is an unexpectedly close Ir?C(o-aryl) contact (2;52(1) Å) involving the “free” L^Ar which compares with an IrC(o-aryl) distance of 2.09(3) Å in Ia or 2.07(3) Å in the ortho-metallated L^Ar ligand of complex IV.     

Synthesis of optically active leukotriene (SRS-A) intermediates

In an approach to SRS-A and analogues thereof, the key (5$\text{S}$, 6$\text{S}$)-epoxy alcohol $\text{9}$ and its 6-epimer $\text{18}$ were prepared starting from $\text{D}$-araboascorbic acid and $\text{L}$-diethyl tartrate, respectively.     

Amino acids derivatives that stabilize secondary structures of polypeptides-- : I. Synthesis of LL-3-amino-2-piperidone-6-carboxylic acid (LL-Acp), a novel beta-turn-forming amino acid

A six-step synthesis is reported of $\text{LL}$-3-amino-2-piperidone-6-carboxylic acid from $\text{L}$-homoserine lactone and the $\text{mono}$-$\text{t}$-butyl ester on $\text{N}$-benzyloxycarbonylaminomalonic acid. Evidence of chiral integrity is discussed.     

Synthesis of detoxininolactone derivatives and the revised absolute stereochemistry of detoxinine

A stereospecific synthesis of acetyl-$\text{L}$-valyl-detoxininolactone has been performed and the absolute stereochemistry of detoxinine has been revised to (2$\text{S}$, 3$\text{R}$, 1′$\text{S}$)-2-(2′-carboxy-1′-hydroxyethyl)-3-hydroxypyrrolidine.     

Synthesis of N-benzoyl-L-ristosamine

The synthesis of N-benzoyl-$\text{L}$-ristosamine (7) from natural tartaric acid through the intermediacy of the δ-$\text{xylo}$ and γ-$\text{ribo}$ lactones (4) and (6) is reported.     

Total synthesis of the disaccharide of bleomycin, 2-0-(α-D-mannopyranosyl)-L-gulopyranose

2-0-(α-$\text{D}$-Mannopyranosyl)-$\text{L}$-gulopyranose, the sugar portion of bleomycin has been synthesized.     

Laureepoxide,new bromo ether from the marine red alga Laurencianipponica Yamada

An interesting bromine containing compound, laureepoxide ($\text{1}$), has been isolated from $\text{L}$. $\text{nipponica}$ Yamada (Rhodomelaceae, Rhodophyta) and its structure has been determined by the chemical degradations and spectral properties.     

Synthesis of N-benzoyl L- and D-2,3,6-trideoxy-3-aminoxylo-hexose from non-carbohydrate precursors

The enantiomeric alcohols ($\text{2}$) and ($\text{11}$), obtained from (2$\text{R}$,3$\text{R}$) tartaric acid and, respectively, $\text{L}$-threonine, have been used to construct the C₆, enantiomeric deoxy amino sugar derivatives ($\text{7}$) and ($\text{12}$)     

Synthesis of 4′-amino-4′-deoxy analog of pantothenic acid

The synthesis of $\text{D}$- and $\text{L}$-N-(4-amino-3, 3-dimethyl-2-hydroxybutyryl)- β-alanine ($\text{7}$) is described. Compound $\text{7}$ is an analog of pantothenic acid in which the 4′-hyroxy group is replaced by amino group. The synthetic sequence leading to $\text{7}$ involved the synthesis $\text{D}$L-4-amino-3,3-dimethyl-2-hydroxybutyric acid and its resolution. Coupling of N-benzyloxycarbonyl N-hydroxysuccinimide ester ($\text{5}$) with β-alanine and followed by removal of the protecting group gave $\text{7}$.