From 7eaa04c6c7e2bab3aed84895424f8a009affb85b Mon Sep 17 00:00:00 2001
From: Dmitrii Polovnev <dmitrii_polovnev@epam.com>
Date: Wed, 12 Jun 2024 18:50:56 +0300
Subject: [PATCH] #4607 - Bugfix (Chain.ts): Correct the definition of
 individual phosphate and linker in `add(1)` (step 2)

---
 .../src/domain/entities/monomer-chains/Chain.ts          | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts b/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts
index 7271a94b20..acf95fdd9b 100644
--- a/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts
+++ b/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts
@@ -74,7 +74,7 @@ export class Chain {
     };
     if (
       monomer instanceof Phosphate &&
-      this.lastNode instanceof Nucleoside &&
+      (!this.lastNode || this.lastNode instanceof Nucleoside) &&
       (!nextMonomer || isNextMonomerNucleosideOrNucleotideOrPeptide())
     ) {
       this.lastSubChain.add(new MonomerSequenceNode(monomer));
@@ -117,7 +117,12 @@ export class Chain {
     return nodes;
   }
 
-  public get lastNode() {
+  public get lastNode():
+    | EmptySequenceNode
+    | MonomerSequenceNode
+    | Nucleoside
+    | Nucleotide
+    | undefined {
     return this.lastSubChain?.lastNode;
   }