1_map.json

{
  "definitions": {
    "Student": {
      "type": "object",
      "properties": {
        "firstName": {
          "type": "string"
        },
        "lastName": {
          "type": "string"
        },
        "age": {
          "type": "integer"
        },
        "properties": {
          "$ref": "Student_Properties"
        }
      }
    },
    "Student_Properties": {
      "type": "object",
      "additionalProperties": {
        "type": "string"
      }
    }
  },
  "$ref": "Student"
}

2_map.ts

export interface Student {
    firstName?: string
    lastName?: string
    age?: number
    properties?: Student_Properties
}

export type Student_Properties = Record<string, string>;