Enantiopure Acids, Esters And Amides via Enzymatic Cleavage Of Thioesters

(1)

Enantiopure Acids, Esters And Amides

via

Enzymatic Cleavage Of Thioesters

HN O S HN O Nu Alcalase(R) Boc Boc HN O S Boc NuH / t-BuOH DBU t-BuOH R Time (h) Yield (%) e.e. (S) (%) Ph- 12 99 >99 PhCH₂- 40 94 99 CH₃CH₂CH₂- 48 91 99 CH₃CH₂- 24 99 >99 CH₃(CH₂)₃CH₂- 110 96 >99

Alcalase CLEA

®

is employed as catalyst:

• high activity

• high stability

• easy separation and reuse

0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00 90,00 0,00 2,00 4,00 6,00 8,00 10,00 12,00 14,00 16,00 18,00 20,00 1^Cycle 5^Cycle 15^Cycle

Cycle

t (h) conv % ee(S) %

1

20

92

99

5

20

82

99

15

20

76

99 Substrate: racemic NBoc‐nVal‐SEt

The catalyst is separated by

centrifugation and directly added

to the successive batch

It is ipossible to restore the full

activity through a simple protocol

• Maximum 50% of conversion • Separation of product from remaining substrate required • Drop in enantiomeric purity as process nears 50% conversion

• A variety of product is obtainable depending on

the nucleophile (acid, esters, amides)

• Potential 100% of conversion

• No separation workup

• Highest enantioselectivity possible kept all over

the reaction course

• Easy separation of the catalyst from the reaction

medium

• It is possible to recycle and reuse the catalyst

First generation system: Enzymatic Kinetic Resolution

• _{Solvent: MTBE/aqueous buffer (biphasic system)}

• _{Catalyst: Alcalase}

®

_{in liquid form}

Second generation system: Enzymatic Dynamic kinetic

Resolution

• _{Solvent: Wet t‐BuOH (monophasic system)}

• _{Catalyst: Alcalase}

®

_{in solid form}

• _Base: DBU

The catalyst

The results:

hydrolysis and amidation

Substrate Product (isolated yields, %)

Product

ee%

DBU [equiv.] Enzyme Loading [w/w] Amine [equiv.] Reaction time [h] 1a 1b (82) 98 2 1:1 2 7 1a 1c (76) 99 4 1:1 1.2 7 1a 1d (89) 98 3 2:1 1.2 5 2a 2b (60) 99 2 1:1 3 30 2a 2c (63) 99 4 4:1 1.2 24 2a 2d (87) 99 2 4:1 1.2 24 3a 3b (66) 99 2 2.5:1 3 168 3a 3c (65) 98 2 2:1 1.2 30 3a 3d (69) 96 2 1:1 1.2 30

…in continuous-flow

Catalyst: Alcalase

®

on silica

After 1h: 78% conv, 98% e.e.

Aim of the work

To find an economically sound enzymatic process for

the synthesis of enantiopure aminoacid derivatives

1. Agosta, E; Caligiuri, A; D’Arrigo, P; Servi, S; Tessaro, D; Canevotti, R; «Enzymatic approach to both enantiomers of N‐Boc hydrophobic amino acids», Tetrahedron: Asymmetry, 17, 13, 1995‐ 1999, 2006

2. Arosio, D; Caligiuri, A; D'Arrigo, P; Pedrocchi‐Fantoni, G; Rossi, C; Saraceno, C; Servi, S; Tessaro, D , «Chemo‐Enzymatic Dynamic Kinetic Resolution of Amino Acid Thioesters», Adv Synyh Catal, 349, 8‐9, 1345‐1348, 2007

3. D'Arrigo, P; Cerioli, L; Servi, S; Viani, F; Tessaro, D; «Synergy between catalysts: enzymes and bases. DKR of non‐natural amino acids derivatives», Catal Sci Technol, 2, 8, 1606‐1616, 2012

D.Tessaro

(1,2)

_{, L. Cerioli}

(1)

_{, P. D’Arrigo}

(1,2)

_, S. Servi

(2)

(1)_{Politecnico di Milano, CMIC Dept., p.za L. da Vinci 32, 20133 Milano, ITALY}