Β-hydroxy Γ-amino Research Articles

Helices with additional H-bonds: crystallographic conformations of α,γ-hybrid peptides helices composed of β-hydroxy γ-amino acids (statines).

β-Hydroxy-γ-amino acids (Statines) are a class of naturally occurring non-ribosomal amino acids frequently found in many peptide natural products. Peptidomimetics constituted with statines have been used as inhibitors for various aspartic acid proteases. In contrast to the synthetic γ-amino acids, very little is known about the folding behavior of these naturally occurring β-hydroxy γ-amino acids. To understand the folding behavior of statines, three α,γ-hybrid peptides P1 (Ac-Aib-γPhe-Aib-(R, S)Phesta-Aib-γPhe-Aib-CONH2 ), P2 (Ac-Aib-γPhe-Aib-(S, S)Phesta-Aib-γPhe-Aib-CONH2 ), and P3 (Ac-Aib-γPhe-Aib-(S, S)Phesta-Aib-(S, S)Phesta-Aib-CONH2 ) were synthesized on solid phase and their helical conformations in single crystals were studied. Results suggest that both syn and anti diastereoisomers of statines can be accommodated into the helix without deviating overall helical conformation of α,γ-hybrid peptides. In comparison with syn diastereoisomer, the anti diastereoisomer was found to be directly involved in the intramolecular H-bonding with the backbone carbonyl groups (i to i + 3) similar to the backbone amide NHs in the helix.

Exploring β-Hydroxy γ-Amino Acids (Statines) in the Design of Hybrid Peptide Foldamers

The synthesis and characterization of syn and anti β-hydroxy γ-amino acid (statine) diastereoisomers, their utilization in the design of hybrid peptide foldamers, and their single crystal conformations are studied.

Practical asymmetric synthesis of β-hydroxy γ-amino acids via complimentary aldol reactions

Orthogonally protected chiral β-hydroxy-γ-amino acids can be accessed in >100 g quantities from readily available starting materials and reagents in three to four steps. These chiral synthons contain two adjacent stereocenters along with suitably protected functional groups ( O-TBS, N-Boc) for downstream reactivity. Implementation of two existing aldol technologies allows rapid access to all possible stereoisomers of 1. The guiding principles during reaction optimization were reaction scalability and operational efficiency. Conversion of the amino acids to a variety of chiral building blocks in one to two steps demonstrates their synthetic utility.

N-Benzyloxymalimide for an easy access to 5-alkyl-3-pyrrolin-2-ones: asymmetric synthesis of the mixed imide substructure of the potent immunosuppressant microcolin B

O-Benzyl- N-benzyloxymalimide 12 has been synthesized as a useful variant of the chiral building blocks 9. The advantage of the malimide 12 over 9 was demonstrated by mild and high-yielding reductive N-deprotection of N-benzyloxylactams 18a– i to give a series of (4 R,5 S)-5-alkyl-4-hydroxy-pyrrolidin-2-ones, which are key intermediates for the asymmetric synthesis of pyrrolidines, pyrrolizidines, and indolizidines, as well as β-hydroxy γ-amino acids. Lactam ent- 11a has been applied to the synthesis of the mixed imide 25, a key intermediate for the total synthesis of microcolin B, which also demonstrated that lactam ent- 11a or 11a can serve as a latent form of the 5-methyl-3-pyrrolin-2-one substructure of majusculamide D 4, deoxymajusculamide D, and the jamaicamides A–C.

Diversity-Oriented Asymmetric Synthesis of Hapalosin: Construction of Three Small C9/C4/C3-Modified Hapalosin Analogue Libraries

A flexible approach to the beta-hydroxy gamma-amino acid residue (fragment C) of hapalosin has been developed on the basis of the the regio- and diastereoselective Grignard reaction. The method allows the introduction of different side chains at the C9 of hapalosin. Asymmetric syntheses of hapalosin (1a), 9-homohapalosin (1b), 9-i-butyl-hapalosin (1c), 8-epi-hapalosin (epi-1a), and three small libraries diversified at C9 (3-member, 1L3), C9/ C4 (9-member, 1L9), or C9/C4/C3 (27-member, 1L27) have been produced using this method.

Ketoreductases in the synthesis of valuable chiral intermediates: application in the synthesis of α-hydroxy β-amino and β-hydroxy γ-amino acids

A general method for the synthesis of β-alkyl α-hydroxy β-amino and α- and γ-alkyl substituted β-hydroxy-γ-amino acids is described. The synthesis of all three classes of amino acids proceeds through a common chiral alcohol intermediate that is generated from a pro-chiral ketone diester via the action of a nicotinamide-dependent ketoreductase. Regioselective chemical or enzymatic hydrolysis followed by rearrangement under Hofmann or Curtius conditions gives the final amino acid products. High yields of single diastereomers of the final amino acids are obtained. Amino acids with both natural and unnatural alkyl substituents can be accessed using this methodology.

A Versatile Approach to N-Boc-statine and N-Boc-norstatine Based on the Reduction of 1-Trialkylsilyl Acetylenic Ketones. Strong Remote Effect of the C(1) Substituent on the Stereoselectivity

An efficient, unified approach to chiral, protected β-hydroxy γ-amino and α-hydroxy β-amino acids derived from Boc-l-leucine has been accomplished on the basis of the oxazaborolidine-controlled, stereoselective reduction of 1-trialkylsilyl acetylenic ketones; stereoselectivity in the reduction step has shown strong dependence upon C(1) substitution.

Synthesis of chiral urethane N-alkoxycarbonyl tetramic acids from urethane N-carboxyanhydrides (UNCAs)

The synthesis of chiral N-protected tetramic acid derivatives which are important precursors of β-hydroxy γ-amino acid under mild conditions is described. Reaction of urethane-N-carboxyanhydrides (UNCAs) with Meldrum's acid in the presence of a tertiary amine, followed by subsequent cyclisation produced tetramic acid derivatives. This procedure is applicable to Boc-, Fmoc- and Z- N-carboxyanhydrides.